diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 5f4cc6bb..058b8011 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -1096,6 +1096,7 @@ class calendar extends rcube_plugin
       $event['recurrence_text'] = $this->_recurrence_text($event['recurrence']);
       if ($event['recurrence']['UNTIL'])
         $event['recurrence']['UNTIL'] = $this->lib->adjust_timezone($event['recurrence']['UNTIL'])->format('c');
+      unset($event['recurrence']['EXCEPTIONS']);
     }
 
     foreach ((array)$event['attachments'] as $k => $attachment) {
@@ -1109,7 +1110,7 @@ class calendar extends rcube_plugin
       'title'       => strval($event['title']),
       'description' => strval($event['description']),
       'location'    => strval($event['location']),
-      'className'   => ($addcss ? 'fc-event-cal-'.asciiwords($event['calendar'], true).' ' : '') . 'fc-event-cat-' . asciiwords(strtolower($event['categories']), true),
+      'className'   => ($addcss ? 'fc-event-cal-'.asciiwords($event['calendar'], true).' ' : '') . 'fc-event-cat-' . asciiwords(strtolower(join('-', (array)$event['categories'])), true),
       'allDay'      => ($event['allday'] == 1),
     ) + $event;
   }
diff --git a/plugins/calendar/drivers/calendar_driver.php b/plugins/calendar/drivers/calendar_driver.php
index a0d0c527..478a08c0 100644
--- a/plugins/calendar/drivers/calendar_driver.php
+++ b/plugins/calendar/drivers/calendar_driver.php
@@ -46,6 +46,7 @@
  *           'COUNT' => 1..n,   // number of times
  *                      // + more properties (see http://www.kanzaki.com/docs/ical/recur.html)
  *          'EXDATE' => array(),  // list of DateTime objects of exception Dates/Times
+ *      'EXCEPTIONS' => array(<event>),  list of event objects which denote exceptions in the recurrence chain
  *    ),
  * 'recurrence_id' => 'ID of the recurrence group',   // usually the ID of the starting event
  *    'categories' => 'Event category',
diff --git a/plugins/calendar/drivers/kolab/kolab_calendar.php b/plugins/calendar/drivers/kolab/kolab_calendar.php
index 45db6383..cfe46f9e 100644
--- a/plugins/calendar/drivers/kolab/kolab_calendar.php
+++ b/plugins/calendar/drivers/kolab/kolab_calendar.php
@@ -312,7 +312,7 @@ class kolab_calendar
    * @return boolean True on success, False on error
    */
 
-  public function update_event($event)
+  public function update_event($event, $exception_id = null)
   {
     $updated = false;
     $old = $this->storage->get_object($event['id']);
@@ -333,6 +333,11 @@ class kolab_calendar
     else {
       $updated = true;
       $this->events[$event['id']] = $this->_to_rcube_event($object);
+
+      // refresh local cache with recurring instances
+      if ($exception_id) {
+        $this->_get_recurring_events($object, $event['start'], $event['end'], $exception_id);
+      }
     }
 
     return $updated;
@@ -413,6 +418,24 @@ class kolab_calendar
       $end->add(new DateInterval($intvl));
     }
 
+    // add recurrence exceptions to output
+    $i = 0;
+    $events = array();
+    if (is_array($event['recurrence']['EXCEPTIONS'])) {
+        foreach ($event['recurrence']['EXCEPTIONS'] as $exception) {
+            $rec_event = $this->_to_rcube_event($exception);
+            $rec_event['id'] = $event['uid'] . '-' . ++$i;
+            $rec_event['recurrence_id'] = $event['uid'];
+            $rec_event['_instance'] = $i;
+            $events[] = $rec_event;
+
+            if ($rec_event['id'] == $event_id) {
+              $this->events[$rec_event['id']] = $rec_event;
+              return $events;
+            }
+        }
+    }
+
     // use libkolab to compute recurring events
     if (class_exists('kolabcalendaring')) {
         $recurrence = new kolab_date_recurrence($object);
@@ -423,8 +446,6 @@ class kolab_calendar
         $recurrence = new calendar_recurrence($this->cal, $event);
     }
 
-    $i = 0;
-    $events = array();
     while ($next_event = $recurrence->next_instance()) {
       $rec_start = $next_event['start']->format('U');
       $rec_end = $next_event['end']->format('U');
diff --git a/plugins/calendar/drivers/kolab/kolab_driver.php b/plugins/calendar/drivers/kolab/kolab_driver.php
index 886f2802..869837fa 100644
--- a/plugins/calendar/drivers/kolab/kolab_driver.php
+++ b/plugins/calendar/drivers/kolab/kolab_driver.php
@@ -565,6 +565,8 @@ class kolab_driver extends calendar_driver
     // keep saved exceptions (not submitted by the client)
     if ($old['recurrence']['EXDATE'])
       $event['recurrence']['EXDATE'] = $old['recurrence']['EXDATE'];
+    if ($old['recurrence']['EXCEPTIONS'])
+      $event['recurrence']['EXCEPTIONS'] = $old['recurrence']['EXCEPTIONS'];
 
     switch ($savemode) {
       case 'new':
@@ -582,26 +584,11 @@ class kolab_driver extends calendar_driver
         break;
         
       case 'current':
-        // modifying the first instance => just move to next occurence
-        if ($master['id'] == $event['id']) {
-          $recurring = reset($storage->_get_recurring_events($event, $event['start'], null, $event['id'].'-1'));
-          $master['start'] = $recurring['start'];
-          $master['end'] = $recurring['end'];
-          if ($master['recurrence']['COUNT'])
-            $master['recurrence']['COUNT']--;
-        }
-        else {  // add exception to master event
-          $master['recurrence']['EXDATE'][] = $old['start'];
-		}
-
-        $storage->update_event($master);
-        
-        // insert new event for this occurence
-        $event += $old;
+        // save as exception to master event
         $event['recurrence'] = array();
-        unset($event['recurrence_id']);
-        $event['uid'] = $this->cal->generate_uid();
-        $success = $storage->insert_event($event);
+        $master['recurrence']['EXCEPTIONS'][] = $event;
+#       $master['recurrence']['EXDATE'][] = $event['start'];
+        $success = $storage->update_event($master);
         break;
         
       case 'future':
@@ -632,6 +619,17 @@ class kolab_driver extends calendar_driver
         }
 
       default:  // 'all' is default
+
+        // save properties to a recurrence exception instance
+        if ($old['recurrence_id']) {
+            $i = $old['_instance'] - 1;
+            if (!empty($master['recurrence']['EXCEPTIONS'][$i])) {
+                $master['recurrence']['EXCEPTIONS'][$i] = $event;
+                $success = $storage->update_event($master, $old['id']);
+                break;
+            }
+        }
+
         $event['id'] = $master['id'];
         $event['uid'] = $master['uid'];
 
diff --git a/plugins/libcalendaring/libcalendaring.php b/plugins/libcalendaring/libcalendaring.php
index 24f98cb4..aa4ec5ef 100644
--- a/plugins/libcalendaring/libcalendaring.php
+++ b/plugins/libcalendaring/libcalendaring.php
@@ -107,6 +107,8 @@ class libcalendaring extends rcube_plugin
             $dt = new DateTime('@'.$td);
         else if (is_string($dt))
             $dt = new DateTime($dt);
+        else
+            return $dt;
 
         $dt->setTimezone($this->timezone);
         return $dt;
diff --git a/plugins/libkolab/lib/kolab_format_event.php b/plugins/libkolab/lib/kolab_format_event.php
index d750f8e0..7efd06d7 100644
--- a/plugins/libkolab/lib/kolab_format_event.php
+++ b/plugins/libkolab/lib/kolab_format_event.php
@@ -30,6 +30,19 @@ class kolab_format_event extends kolab_format_xcal
     protected $read_func = 'readEvent';
     protected $write_func = 'writeEvent';
 
+    /**
+     * Default constructor
+     */
+    function __construct($data = null, $version = 3.0)
+    {
+        parent::__construct(is_string($data) ? $data : null, $version);
+
+        // got an Event object as argument
+        if (is_object($data) && is_a($data, $this->objclass)) {
+            $this->obj = $data;
+            $this->loaded = true;
+        }
+    }
 
     /**
      * Clones into an instance of libcalendaring's extended EventCal class
@@ -90,6 +103,18 @@ class kolab_format_event extends kolab_format_xcal
         }
         $this->obj->setAttachments($vattach);
 
+        // save recurrence exceptions
+        if ($object['recurrence']['EXCEPTIONS']) {
+            $vexceptions = new vectorevent;
+            foreach((array)$object['recurrence']['EXCEPTIONS'] as $exception) {
+                $exevent = new kolab_format_event;
+                $exevent->set($this->compact_exception($exception, $object));  // only save differing values
+                $exevent->obj->setRecurrenceID(self::get_datetime($exception['start'], null, true), false);
+                $vexceptions->push($exevent->obj);
+            }
+            $this->obj->setExceptions($vexceptions);
+        }
+
         // cache this data
         $this->data = $object;
         unset($this->data['_formatobj']);
@@ -160,6 +185,18 @@ class kolab_format_event extends kolab_format_xcal
             }
         }
 
+        // read exception event objects
+        if ($exceptions = $this->obj->exceptions()) {
+            for ($i=0; $i < $exceptions->size(); $i++) {
+                if (($exobj = $exceptions->get($i))) {
+                    $exception = new kolab_format_event($exobj);
+                    if ($exception->is_valid()) {
+                        $object['recurrence']['EXCEPTIONS'][] = $this->expand_exception($exception->to_array(), $object);
+                    }
+                }
+            }
+        }
+
         // merge with additional data, e.g. attachments from the message
         if ($data) {
             foreach ($data as $idx => $value) {
@@ -195,4 +232,45 @@ class kolab_format_event extends kolab_format_xcal
         return $tags;
     }
 
+    /**
+     * Reduce the exception container to attributes which differ from the master event
+     */
+    private function compact_exception($exception, $master)
+    {
+      static $mandatory = array('uid','created','start');
+      static $forbidden = array('recurrence','attendees','sequence');
+
+      $out = $exception;
+      foreach ($exception as $prop => $val) {
+        if (in_array($prop, $mandatory))
+          continue;
+
+        if (is_object($exception[$prop]) && is_a($exception[$prop], 'DateTime'))
+          $equals = $exception[$prop] <> $master[$prop];
+        else
+          $equals = $exception[$prop] == $master[$prop];
+
+        if ($equals || in_array($prop, $forbidden)) {
+          unset($out[$prop]);
+        }
+      }
+
+      return $out;
+    }
+
+    /**
+     * Copy attributes not specified by the exception from the master event
+     */
+    private function expand_exception($exception, $master)
+    {
+      static $forbidden = array('recurrence');
+
+      foreach ($master as $prop => $value) {
+        if (empty($exception[$prop]) && !in_array($prop, $forbidden))
+          $exception[$prop] = $value;
+      }
+
+      return $exception;
+    }
+
 }
diff --git a/plugins/libkolab/lib/kolab_format_xcal.php b/plugins/libkolab/lib/kolab_format_xcal.php
index a6450afb..bc50c4b8 100644
--- a/plugins/libkolab/lib/kolab_format_xcal.php
+++ b/plugins/libkolab/lib/kolab_format_xcal.php
@@ -113,7 +113,7 @@ abstract class kolab_format_xcal extends kolab_format
         );
 
         // read organizer and attendees
-        if ($organizer = $this->obj->organizer()) {
+        if (($organizer = $this->obj->organizer()) && ($organizer->email() || $organizer->name())) {
             $object['organizer'] = array(
                 'email' => $organizer->email(),
                 'name' => $organizer->name(),
@@ -170,9 +170,9 @@ abstract class kolab_format_xcal extends kolab_format
                 $object['recurrence']['BYMONTH'] = join(',', self::vector2array($bymonth));
             }
 
-            if ($exceptions = $this->obj->exceptionDates()) {
-                for ($i=0; $i < $exceptions->size(); $i++) {
-                    if ($exdate = self::php_datetime($exceptions->get($i)))
+            if ($exdates = $this->obj->exceptionDates()) {
+                for ($i=0; $i < $exdates->size(); $i++) {
+                    if ($exdate = self::php_datetime($exdates->get($i)))
                         $object['recurrence']['EXDATE'][] = $exdate;
                 }
             }