diff --git a/calendar/inc/class.calendar_bo.inc.php b/calendar/inc/class.calendar_bo.inc.php
index 1708591783..f80c7de0cb 100644
--- a/calendar/inc/class.calendar_bo.inc.php
+++ b/calendar/inc/class.calendar_bo.inc.php
@@ -1937,33 +1937,33 @@ class calendar_bo
 		$etag .= ':'.$entry['modified'];
 
 		// include exception etags into our own etag, if exceptions are included
-		if ($client_share_uid_excpetions && !empty($entry['uid']) &&
+		if ($client_share_uid_excpetions && //!empty($entry['uid']) &&
 			$entry['recur_type'] != MCAL_RECUR_NONE && $entry['recur_exception'])
 		{
-			$events =& $this->search(array(
-				//'query' => array('cal_uid' => $entry['uid']),
-				'query' => array('cal_reference' => $entry['id']),
-				'filter' => 'owner',  // return all possible entries
-				'daywise' => false,
-				'enum_recuring' => false,
-				'date_format' => 'server',
-				'no_total' => true,
-			));
-			foreach($events as $k => &$recurrence)
+			foreach($this->so->get_cal_data(array(
+				'cal_reference' => $entry['id'],
+			), 'cal_id,cal_reference,cal_etag,cal_modified'.(!$master_only ? ',cal_user_modified' : '')) as $recurrence)
 			{
+				$recurrence = egw_db::strip_array_keys($data, 'cal_');
 				if ($recurrence['reference'] && $recurrence['id'] != $entry['id'])	// ignore series master
 				{
-					$exception_etag = $this->get_etag($recurrence, $nul);
+					// modified need to be max from modified and user_modified
+					if (!$master_only && $recurrence['modified'] < $recurrence['user_modified'])
+					{
+						$recurrence['modified'] = $recurrence['user_modified'];
+					}
+					$exception_etag = $this->get_etag($recurrence);
 					// if $master_only, only add cal_etag, not max. user modification date
 					if ($master_only) list(,$exception_etag) = explode(':',$exception_etag);
 
-					$exception_etags .= ':'.$this->get_etag($recurrence, $nul);
+					$exception_etags .= ':'.$exception_etag;
 				}
 			}
 			if ($exception_etags)
 			{
 				$etag .= ':'.md5($exception_etags);	// limit size, as there can be many exceptions
 			}
+			//error_log(__METHOD__."($entry[id]: $entry[title]) returning $etag ".function_backtrace());
 		}
 		//error_log(__METHOD__ . "($entry[id],$client_share_uid_excpetions) entry=".array2string($entry)." --> etag=$etag");
 		return $etag;
diff --git a/calendar/inc/class.calendar_so.inc.php b/calendar/inc/class.calendar_so.inc.php
index d94044b919..b717dec2a4 100644
--- a/calendar/inc/class.calendar_so.inc.php
+++ b/calendar/inc/class.calendar_so.inc.php
@@ -370,6 +370,29 @@ class calendar_so
 			$where,__LINE__,__FILE__,false,'','calendar',0,'JOIN egw_cal ON egw_cal.cal_id=egw_cal_user.cal_id')->fetchColumn();
 	}
 
+	/**
+	 * Query calendar main table and return iterator of query
+	 *
+	 * Use as: foreach(get_cal_data() as $data) { $data = egw_db::strip_array_keys($data, 'cal_'); // do something with $data
+	 *
+	 * @param array $query filter, keys have to use 'cal_' prefix
+	 * @param string|array $cols='cal_id,cal_reference,cal_etag,cal_modified,cal_user_modified' cols to query
+	 * @return Iterator as egw_db::select
+	 */
+	function get_cal_data(array $query, $cols='cal_id,cal_reference,cal_etag,cal_modified,cal_user_modified', $include_user_modified=false)
+	{
+		if (!is_array($cols)) $cols = explode(',', $cols);
+
+		// special handling of cal_user_modified "pseudo" column
+		if (($key = array_search('cal_user_modified', $cols)) !== false)
+		{
+			$cols[$key] = $this->db->unix_timestamp('(SELECT MAX(cal_user_modified) FROM '.
+				$this->user_table.' WHERE '.$this->cal_table.'.cal_id='.$this->user_table.'.cal_id)').
+				' AS cal_user_modified';
+		}
+		return $this->db->select($this->cal_table, $cols, $query, __LINE__, __FILE__);
+	}
+
 	/**
 	 * generate SQL to filter after a given category (incl. subcategories)
 	 *
diff --git a/phpgwapi/inc/class.groupdav_handler.inc.php b/phpgwapi/inc/class.groupdav_handler.inc.php
index e3aea35f99..947457458b 100644
--- a/phpgwapi/inc/class.groupdav_handler.inc.php
+++ b/phpgwapi/inc/class.groupdav_handler.inc.php
@@ -538,8 +538,12 @@ abstract class groupdav_handler
 	 */
 	public function add_resource($path, array $entry, array $props)
 	{
+		// only run get_etag, if we really need it, as it might be expensive (eg. calendar)
+		if (!isset($props['getetag']))
+		{
+			$props['getetag'] = $this->get_etag($entry);
+		}
 		foreach(array(
-			'getetag' => $this->get_etag($entry),
 			'getcontenttype' => 'text/calendar',
 			'getlastmodified' => $entry['modified'],
 			'displayname' => $entry['title'],