diff --git a/plugins/libkolab/lib/kolab_format_event.php b/plugins/libkolab/lib/kolab_format_event.php
index 596d0da3..c233f444 100644
--- a/plugins/libkolab/lib/kolab_format_event.php
+++ b/plugins/libkolab/lib/kolab_format_event.php
@@ -26,7 +26,7 @@ class kolab_format_event extends kolab_format_xcal
 {
     public $CTYPEv2 = 'application/x-vnd.kolab.event';
 
-    public static $scheduling_properties = array('start', 'end', 'allday', 'location', 'status', 'cancelled');
+    public $scheduling_properties = array('start', 'end', 'allday', 'location', 'status', 'cancelled');
 
     protected $objclass = 'Event';
     protected $read_func = 'readEvent';
diff --git a/plugins/libkolab/lib/kolab_format_task.php b/plugins/libkolab/lib/kolab_format_task.php
index ee0ca6a9..52744d45 100644
--- a/plugins/libkolab/lib/kolab_format_task.php
+++ b/plugins/libkolab/lib/kolab_format_task.php
@@ -26,7 +26,7 @@ class kolab_format_task extends kolab_format_xcal
 {
     public $CTYPEv2 = 'application/x-vnd.kolab.task';
 
-    public static $scheduling_properties = array('start', 'due', 'summary', 'status');
+    public $scheduling_properties = array('start', 'due', 'summary', 'status');
 
     protected $objclass = 'Todo';
     protected $read_func = 'readTodo';
diff --git a/plugins/libkolab/lib/kolab_format_xcal.php b/plugins/libkolab/lib/kolab_format_xcal.php
index 6624b025..7d077b7c 100644
--- a/plugins/libkolab/lib/kolab_format_xcal.php
+++ b/plugins/libkolab/lib/kolab_format_xcal.php
@@ -29,7 +29,8 @@ abstract class kolab_format_xcal extends kolab_format
     public $CTYPE = 'application/calendar+xml';
 
     public static $fulltext_cols = array('title', 'description', 'location', 'attendees:name', 'attendees:email', 'categories');
-    public static $scheduling_properties = array('start', 'end', 'location');
+
+    public $scheduling_properties = array('start', 'end', 'location');
 
     protected $sensitivity_map = array(
         'public'       => kolabformat::ClassPublic,
@@ -315,7 +316,7 @@ abstract class kolab_format_xcal extends kolab_format
                 // increment sequence when updating properties relevant for scheduling.
                 // RFC 5545: "It is incremented [...] each time the Organizer makes a significant revision to the calendar component."
                 // TODO: make the list of properties considered 'significant' for scheduling configurable
-                foreach (self::$scheduling_properties as $prop) {
+                foreach ($this->scheduling_properties as $prop) {
                     $a = $old[$prop];
                     $b = $object[$prop];
                     if ($object['allday'] && ($prop == 'start' || $prop == 'end') && $a instanceof DateTime && $b instanceof DateTime) {
diff --git a/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php b/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php
index 68840838..ef8f31db 100644
--- a/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php
+++ b/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php
@@ -904,7 +904,7 @@ class tasklist_kolab_driver extends tasklist_driver
 
         $object['_owner'] = $identity['email'];
 
-        unset($object['tempid'], $object['raw'], $object['list'], $object['flagged'], $object['tags']);
+        unset($object['tempid'], $object['raw'], $object['list'], $object['flagged'], $object['tags'], $object['sequence']);
         return $object;
     }