diff --git a/plugins/calendar/drivers/database/database_driver.php b/plugins/calendar/drivers/database/database_driver.php
index 8c22bb0a..0038218c 100644
--- a/plugins/calendar/drivers/database/database_driver.php
+++ b/plugins/calendar/drivers/database/database_driver.php
@@ -299,7 +299,7 @@ class database_driver extends calendar_driver
       $old = $this->get_event($event);
       
       // increment sequence number
-      if ($old['sequence'])
+      if ($old['sequence'] && empty($event['sequence']))
         $event['sequence'] = max($event['sequence'], $old['sequence']+1);
       
       // modify a recurring event, check submitted savemode to do the right things
diff --git a/plugins/calendar/drivers/kolab/kolab_driver.php b/plugins/calendar/drivers/kolab/kolab_driver.php
index 3e0b8b0b..516452fb 100644
--- a/plugins/calendar/drivers/kolab/kolab_driver.php
+++ b/plugins/calendar/drivers/kolab/kolab_driver.php
@@ -370,8 +370,10 @@ class kolab_driver extends calendar_driver
    */
   public function move_event($event)
   {
-    if (($storage = $this->calendars[$event['calendar']]) && ($ev = $storage->get_event($event['id'])))
+    if (($storage = $this->calendars[$event['calendar']]) && ($ev = $storage->get_event($event['id']))) {
+      unset($ev['sequence']);
       return $this->update_event($event + $ev);
+    }
 
     return false;
   }
@@ -384,8 +386,10 @@ class kolab_driver extends calendar_driver
    */
   public function resize_event($event)
   {
-    if (($storage = $this->calendars[$event['calendar']]) && ($ev = $storage->get_event($event['id'])))
+    if (($storage = $this->calendars[$event['calendar']]) && ($ev = $storage->get_event($event['id']))) {
+      unset($ev['sequence']);
       return $this->update_event($event + $ev);
+    }
 
     return false;
   }
diff --git a/plugins/libkolab/lib/kolab_format_xcal.php b/plugins/libkolab/lib/kolab_format_xcal.php
index ff10a100..34f2d81c 100644
--- a/plugins/libkolab/lib/kolab_format_xcal.php
+++ b/plugins/libkolab/lib/kolab_format_xcal.php
@@ -237,7 +237,8 @@ abstract class kolab_format_xcal extends kolab_format
         parent::set($object);
 
         // increment sequence on updates
-        $object['sequence'] = !$is_new ? $this->obj->sequence()+1 : 0;
+        if (empty($object['sequence']))
+            $object['sequence'] = !$is_new ? $this->obj->sequence()+1 : 0;
         $this->obj->setSequence($object['sequence']);
 
         $this->obj->setSummary($object['title']);