diff --git a/calendar/inc/class.calendar_boupdate.inc.php b/calendar/inc/class.calendar_boupdate.inc.php
index 4d057d0e3d..8f01597d3a 100644
--- a/calendar/inc/class.calendar_boupdate.inc.php
+++ b/calendar/inc/class.calendar_boupdate.inc.php
@@ -143,7 +143,7 @@ class calendar_boupdate extends calendar_bo
 		if ($new_event)
 		{
 			$event['created'] = $this->now_su;
-			$event['creator'] = $GLOBALS['egw_info']['user']['account_id'];
+			$event['creator'] = $this->user;
 			$old_event = array();
 		}
 		else
@@ -339,7 +339,7 @@ class calendar_boupdate extends calendar_bo
 		if ($touch_modified)
 		{
 			$event['modified'] = $this->now_su;	// we are still in user-time
-			$event['modifier'] = $GLOBALS['egw_info']['user']['account_id'];
+			$event['modifier'] = $this->user;
 		}
 		//echo "saving $event[id]="; _debug_array($event);
 		$event2save = $event;
@@ -927,6 +927,16 @@ class calendar_boupdate extends calendar_bo
 				$event['alarm'][$id]['time'] = $this->date2ts($alarm['time'],true);
 			}
 		}
+		if (!isset($event['modified']))
+		{
+			$event['modified'] = $this->now;
+			$event['modifier'] = $this->user;
+		}
+		if (empty($event['id']) && !isset($event['created']))
+		{
+			$event['created'] = $this->now;
+			$event['creator'] = $this->user;
+		}
 		$set_recurrences = false;
 		$set_recurrences_start = 0;
 		if (($cal_id = $this->so->save($event,$set_recurrences,$set_recurrences_start,0,$event['etag'])) && $set_recurrences && $event['recur_type'] != MCAL_RECUR_NONE)
@@ -936,7 +946,7 @@ class calendar_boupdate extends calendar_bo
 			unset($save_event['participants']);
 			$this->set_recurrences($save_event, $set_recurrences_start);
 		}
-		if ($updateTS) $GLOBALS['egw']->contenthistory->updateTimeStamp('calendar',$cal_id,$event['id'] ? 'modify' : 'add',time());
+		if ($updateTS) $GLOBALS['egw']->contenthistory->updateTimeStamp('calendar', $cal_id, $event['id'] ? 'modify' : 'add', $this->now);
 
 		// Update history
 		$tracking = new calendar_tracking($this);
@@ -1138,8 +1148,12 @@ class calendar_boupdate extends calendar_bo
 				is_numeric($uid)?$uid:substr($uid,1),$status,
 				$recur_date?$this->date2ts($recur_date,true):0,$role)))
 		{
-			if ($updateTS) $GLOBALS['egw']->contenthistory->updateTimeStamp('calendar',$cal_id,'modify',time());
-
+			if ($updateTS)
+			{
+				$GLOBALS['egw']->content ->updateTimeStamp('calendar', $cal_id, 'modify', $this->now);
+				$this->so->updateModified($cal_id, $this->now, $this->user);
+			}
+			
 			static $status2msg = array(
 				'R' => MSG_REJECTED,
 				'T' => MSG_TENTATIVE,
@@ -1238,7 +1252,7 @@ class calendar_boupdate extends calendar_bo
 					}
 				}
 			}
-			$GLOBALS['egw']->contenthistory->updateTimeStamp('calendar',$cal_id,'delete',time());
+			$GLOBALS['egw']->contenthistory->updateTimeStamp('calendar', $cal_id, 'delete', $this->now);
 		}
 		else
 		{
@@ -1446,7 +1460,8 @@ class calendar_boupdate extends calendar_bo
 		}
 		$alarm['time'] = $this->date2ts($alarm['time'],true);	// user to server-time
 
-		$GLOBALS['egw']->contenthistory->updateTimeStamp('calendar',$cal_id, 'modify', time());
+		$GLOBALS['egw']->contenthistory->updateTimeStamp('calendar', $cal_id, 'modify', $this->now);
+		$this->so->updateModified($cal_id, $this->now, $this->user);
 
 		return $this->so->save_alarm($cal_id,$alarm, $this->now);
 	}
@@ -1466,7 +1481,8 @@ class calendar_boupdate extends calendar_bo
 			return false;	// no rights to delete the alarm
 		}
 
-		$GLOBALS['egw']->contenthistory->updateTimeStamp('calendar',$cal_id, 'modify', time());
+		$GLOBALS['egw']->contenthistory->updateTimeStamp('calendar', $cal_id, 'modify', $this->now);
+		$this->so->updateModified($cal_id, $this->now, $this->user);
 
 		return $this->so->delete_alarm($id, $this->now);
 	}
diff --git a/calendar/inc/class.calendar_groupdav.inc.php b/calendar/inc/class.calendar_groupdav.inc.php
index e4da86a4ff..f2c46a5904 100644
--- a/calendar/inc/class.calendar_groupdav.inc.php
+++ b/calendar/inc/class.calendar_groupdav.inc.php
@@ -107,8 +107,8 @@ class calendar_groupdav extends groupdav_handler
 		// ToDo: add parameter to only return id & etag
 		$filter = array(
 			'users' => $user,
-			'start' => time()-100*24*3600,	// default one month back -30 breaks all sync recurrences
-			'end' => time()+365*24*3600,	// default one year into the future +365
+			'start' => $this->bo->now - 100*24*3600,	// default one month back -30 breaks all sync recurrences
+			'end' => $this->bo->now + 365*24*3600,	// default one year into the future +365
 			'enum_recuring' => false,
 			'daywise' => false,
 			'date_format' => 'server',
@@ -756,7 +756,39 @@ error_log(__METHOD__."($path,,".array2string($start).") filter=".array2string($f
 	 */
 	public function getctag($path,$user)
 	{
-		$ctag = $GLOBALS['egw']->contenthistory->getLastChange('calendar');
+		$filter = array(
+			'users' => $user,
+			'start' => $this->bo->now - 100*24*3600,	// default one month back -30 breaks all sync recurrences
+			'end' => $this->bo->now + 365*24*3600,	// default one year into the future +365
+			'enum_recuring' => false,
+			'daywise' => false,
+			'date_format' => 'server',
+			'cols'		=> array('cal_modified'),
+			'order'     => 'cal_modified DESC',
+			'num_rows'	=> 1,
+		);
+		
+		if ($path == '/calendar/')
+		{
+			$filter['filter'] = 'owner';
+		}
+		else
+		{
+			$filter['filter'] = 'default'; // not rejected
+		}
+		
+		if (($events =& $this->bo->search($filter)))
+		{
+			foreach ($events as $event)
+			{
+				$ctag = $event['cal_modified'];
+				break;
+			}
+		}
+		else
+		{
+			$ctag = '0';
+		}
 
 		if ($this->debug > 1) error_log(__FILE__.'['.__LINE__.'] '.__METHOD__. "($path)[$user] = $ctag");
 		
diff --git a/calendar/inc/class.calendar_so.inc.php b/calendar/inc/class.calendar_so.inc.php
index 410fb29d2a..38ec4eb68d 100644
--- a/calendar/inc/class.calendar_so.inc.php
+++ b/calendar/inc/class.calendar_so.inc.php
@@ -2190,4 +2190,19 @@ ORDER BY cal_user_type, cal_usre_id
 		}
 		return new egw_time($time->format('Y-m-d 00:00:00'), $timezone);
 	}
+	
+	/**
+	 * Udates the modification timestamp 
+	 *
+	 * @param id		event id
+	 * @param time		new timestamp
+	 * @param modifier	uid of the modifier
+	 * 
+	 */
+	function updateModified($id, $time, $modifier)
+	{
+		$this->db->update($this->cal_table,
+			array('cal_modified' => $time, 'cal_modifier' => $modifier),
+			array('cal_id' => $id), __LINE__,__FILE__, 'calendar');
+	}
 }