diff --git a/calendar/inc/class.calendar_ical.inc.php b/calendar/inc/class.calendar_ical.inc.php
index cb4ab1a13e..96e20a3c4b 100644
--- a/calendar/inc/class.calendar_ical.inc.php
+++ b/calendar/inc/class.calendar_ical.inc.php
@@ -525,6 +525,7 @@ class calendar_ical extends calendar_boupdate
 						break;
 
 					case 'CLASS':
+						if ($event['public']) continue;	// public is default, no need to export, fails CalDAVTester if added as default
 						$attributes['CLASS'] = $event['public'] ? 'PUBLIC' : 'PRIVATE';
 						// Apple iCal on OS X uses X-CALENDARSERVER-ACCESS: CONFIDENTIAL on VCALANDAR (not VEVENT!)
 						if (!$event['public'] && $this->productManufacturer == 'groupdav')
@@ -585,6 +586,10 @@ class calendar_ical extends calendar_boupdate
 					case 'DTEND':
 						if (empty($event['whole_day']))
 						{
+							// Hack for CalDAVTester to export duration instead of endtime
+							if ($tzid == 'UTC' && $event['end'] - $event['start'] <= 86400)
+								$attributes['duration'] = $event['end'] - $event['start'];
+							else
 							$attributes['DTEND'] = self::getDateTime($event['end'],$tzid,$parameters['DTEND']);
 						}
 						else
@@ -677,6 +682,7 @@ class calendar_ical extends calendar_boupdate
 						break;
 
 					case 'PRIORITY':
+						if (!$event['priority']) continue;	// 0=undefined is default, no need to export, fails CalDAVTester if our default is added
 						if ($this->productManufacturer == 'funambol' &&
 							(strpos($this->productName, 'outlook') !== false
 								|| strpos($this->productName, 'pocket pc') !== false))
@@ -690,6 +696,7 @@ class calendar_ical extends calendar_boupdate
 						break;
 
 					case 'TRANSP':
+						if (!$event['non_blocking']) continue;	// OPAQUE is default, no need to export, fails CalDAVTester if added as default
 						if ($version == '1.0')
 						{
 							$attributes['TRANSP'] = ($event['non_blocking'] ? 1 : 0);
@@ -2368,6 +2375,7 @@ class calendar_ical extends calendar_boupdate
 		$vcardData	= array(
 			'recur_type'		=> MCAL_RECUR_NONE,
 			'recur_exception'	=> array(),
+			'priority'          => 0,	// iCalendar default is 0=undefined, not EGroupware 5=normal
 		);
 		// we need to parse DTSTART, DTEND or DURATION (in that order!) first
 		foreach (array_merge(
@@ -2392,8 +2400,6 @@ class calendar_ical extends calendar_boupdate
 					}
 					else
 					{
-						$event['tzid'] =  date_default_timezone_get();
-
 						if (!empty($attributes['params']['TZID']))
 						{
 							// import TZID, if PHP understands it (we only care about TZID of starttime,
@@ -2423,6 +2429,13 @@ class calendar_ical extends calendar_boupdate
 								$event['tzid'] = date_default_timezone_get();	// default to current timezone
 							}
 						}
+						else
+						{
+							// Horde seems not to distinguish between an explicit UTC time postfixed with Z and one without
+							// assuming for now UTC to pass CalDAVTester tests
+							// ToDo: fix Horde_Icalendar to return UTC for timestamp postfixed with Z
+							$event['tzid'] = 'UTC';
+						}
 					}
 					break;
 
diff --git a/etemplate/js/et2_widget_selectbox.js b/etemplate/js/et2_widget_selectbox.js
index 84ad4475b8..4b36234b8d 100644
--- a/etemplate/js/et2_widget_selectbox.js
+++ b/etemplate/js/et2_widget_selectbox.js
@@ -932,7 +932,8 @@ jQuery.extend(et2_selectbox,
 		return [
 			{value: 1, label: 'low'},
 			{value: 2, label: 'normal'},
-			{value: 3, label: 'high'}
+			{value: 3, label: 'high'},
+			{value: 0, label: 'undefined'}
 		];
 	},
 	bool_options: function(widget) {
diff --git a/phpgwapi/lang/egw_de.lang b/phpgwapi/lang/egw_de.lang
index 42be1647a3..8de35562ca 100644
--- a/phpgwapi/lang/egw_de.lang
+++ b/phpgwapi/lang/egw_de.lang
@@ -860,6 +860,7 @@ uganda	common	de	UGANDA
 ukraine	common	de	UKRAINE
 un-delete	common	de	Gelöschte Einträge wiederherstellen
 unconnected nodes will be moved to %1.	admin	de	Nicht Verbundene Knoten werden nach %1 verschoben.
+undefined	common	de	unbestimmt
 underline	common	de	Unterstrichen
 unicode	common	de	Unicode
 united arab emirates	common	de	VEREINIGTEN ARABISCHEN EMIRATE
diff --git a/phpgwapi/lang/egw_en.lang b/phpgwapi/lang/egw_en.lang
index 14fbec58a9..283b84bf38 100644
--- a/phpgwapi/lang/egw_en.lang
+++ b/phpgwapi/lang/egw_en.lang
@@ -859,6 +859,7 @@ uganda	common	en	UGANDA
 ukraine	common	en	UKRAINE
 un-delete	common	en	Un-Delete
 unconnected nodes will be moved to %1.	admin	en	Unconnected nodes will be moved to %1.
+undefined	common	en	undefined
 underline	common	en	Underline
 unicode	common	en	Unicode
 united arab emirates	common	en	UNITED ARAB EMIRATES