diff --git a/addressbook/inc/class.addressbook_export_contacts_csv.inc.php b/addressbook/inc/class.addressbook_export_contacts_csv.inc.php
index b1d67d003c..dd4ef9e797 100644
--- a/addressbook/inc/class.addressbook_export_contacts_csv.inc.php
+++ b/addressbook/inc/class.addressbook_export_contacts_csv.inc.php
@@ -251,11 +251,11 @@ class addressbook_export_contacts_csv implements importexport_iface_export_plugi
 			{
 				if(is_array($_contact) && $_contact['id'])
 				{
-					$contact_ids[] = $_contact['id'];
+					$contact_ids[] = $_contact['account_id'] ? $_contact['account_id'] : 'c'.$_contact['id'];
 				}
 				else
 				{
-					$contact_ids[] = $contact;
+					$contact_ids[] = 'c'.$contact;
 				}
 			}
 			$events = $this->ui->read_calendar($contact_ids, false);
diff --git a/addressbook/inc/class.addressbook_ui.inc.php b/addressbook/inc/class.addressbook_ui.inc.php
index c87cc91630..af31dbf5c0 100644
--- a/addressbook/inc/class.addressbook_ui.inc.php
+++ b/addressbook/inc/class.addressbook_ui.inc.php
@@ -1640,6 +1640,7 @@ window.egw_LAB.wait(function() {
 			$columsel = $this->prefs['nextmatch-addressbook.'.($do_email ? 'email' : 'index').'.rows'];
 			$available_distib_lists=$this->get_lists(Acl::READ);
 			$columselection = $columsel && !$query['csv_export'] ? explode(',',$columsel) : array();
+			$ids = $calendar_participants = array();
 			if (!$id_only && $rows)
 			{
 				$show_custom_fields = (!$columselection || in_array('customfields',$columselection) || $query['csv_export']) && $this->customfields;
@@ -1650,6 +1651,7 @@ window.egw_LAB.wait(function() {
 					foreach($rows as $val)
 					{
 						$ids[] = $val['id'];
+						$calendar_participants[$val['id']] = $val['account_id'] ? $val['account_id'] : 'c'.$val['id'];
 					}
 					if ($show_custom_fields)
 					{
@@ -1659,7 +1661,7 @@ window.egw_LAB.wait(function() {
 						}
 						$customfields = $this->read_customfields($ids,$selected_cfs);
 					}
-					if ($show_calendar && !empty($ids)) $calendar = $this->read_calendar($ids);
+					if ($show_calendar && !empty($ids)) $calendar = $this->read_calendar($calendar_participants);
 					// distributionlist memership for the entrys
 					//_debug_array($this->get_lists(Acl::EDIT));
 					if ($show_distributionlist && $available_distib_lists)
@@ -1766,9 +1768,9 @@ window.egw_LAB.wait(function() {
 					$row['distrib_lists'] = implode("\n",array_values($distributionlist[$row['id']]));
 					//if ($show_distributionlist) $readonlys['distrib_lists'] =true;
 				}
-				if (isset($calendar[$row['id']]))
+				if (isset($calendar[$calendar_participants[$row['id']]]))
 				{
-					foreach($calendar[$row['id']] as $name => $data)
+					foreach($calendar[$calendar_participants[$row['id']]] as $name => $data)
 					{
 						$row[$name] = $data;
 					}
@@ -2234,7 +2236,7 @@ window.egw_LAB.wait(function() {
 		if ($content['id'])
 		{
 			// last and next calendar date
-			list(,$dates) = each($this->read_calendar(array($content['id']),false));
+			list(,$dates) = each($this->read_calendar(array($content['account_id'] ? $content['account_id'] : 'c'.$content['id']),false));
 			if(is_array($dates)) $content += $dates;
 		}
 		// Avoid ID conflict with tree & selectboxes
@@ -2738,7 +2740,7 @@ window.egw_LAB.wait(function() {
 		if ($this->config['private_cf_tab']) $content['no_private_cfs'] = 0;
 
 		// last and next calendar date
-		if (!empty($content['id'])) list(,$dates) = each($this->read_calendar(array($content['id']),false));
+		if (!empty($content['id'])) list(,$dates) = each($this->read_calendar(array($content['account_id'] ? $content['account_id'] : 'c'.$content['id']),false));
 		if(is_array($dates)) $content += $dates;
 
 		// Disable importexport
diff --git a/addressbook/js/app.js b/addressbook/js/app.js
index a4a2eb010d..b41f3e3e61 100644
--- a/addressbook/js/app.js
+++ b/addressbook/js/app.js
@@ -253,7 +253,17 @@ app.classes.addressbook = AppJS.extend(
 			}
 			else
 			{
-				extras.owner.push('c'+ids);
+				// Check to see if this is a user account, we prefer to use
+				// account ID in calendar
+				var data = this.egw.dataGetUIDdata(_senders[i].id);
+				if(data && data.data && data.data.account_id)
+				{
+					extras.owner.push(data.data.account_id);
+				}
+				else
+				{
+					extras.owner.push('c'+ids);
+				}
 			}
 		}
 
diff --git a/api/src/Contacts.php b/api/src/Contacts.php
index bcac1a5556..aace1be91f 100755
--- a/api/src/Contacts.php
+++ b/api/src/Contacts.php
@@ -1601,21 +1601,14 @@ class Contacts extends Contacts\Storage
 	/**
 	 * Read the next and last event of given contacts
 	 *
-	 * @param array $ids contact_id's
+	 * @param array $uids participant IDs.  Contacts should be c<contact_id>, user accounts <account_id>
 	 * @param boolean $extra_title =true if true, use a short date only title and put the full title as extra_title (tooltip)
 	 * @return array
 	 */
-	function read_calendar($ids,$extra_title=true)
+	function read_calendar($uids,$extra_title=true)
 	{
 		if (!$GLOBALS['egw_info']['user']['apps']['calendar']) return array();
 
-		$uids = array();
-		foreach($ids as $id)
-		{
-			if (is_numeric($id)) $uids[] = 'c'.$id;
-		}
-		if (!$uids) return array();
-
 		$bocal = new calendar_bo();
 		$events = $bocal->search(array(
 			'users' => $uids,
@@ -1629,17 +1622,16 @@ class Contacts extends Contacts\Storage
 		{
 			foreach($event['participants'] as $uid => $status)
 			{
-				if ($uid[0] != 'c' || ($status == 'R' && !$GLOBALS['egw_info']['user']['preferences']['calendar']['show_rejected']))
+				if ($status == 'R' && !$GLOBALS['egw_info']['user']['preferences']['calendar']['show_rejected'])
 				{
 					continue;
 				}
-				$id = (int)substr($uid,1);
 
 				if ($event['start'] < $this->now_su)	// past event --> check for last event
 				{
-					if (!isset($calendars[$id]['last_event']) || $event['start'] > $calendars[$id]['last_event'])
+					if (!isset($calendars[$uid]['last_event']) || $event['start'] > $calendars[$uid]['last_event'])
 					{
-						$calendars[$id]['last_event'] = $event['start'];
+						$calendars[$uid]['last_event'] = $event['start'];
 						$link = array(
 							'id' => $event['id'],
 							'app' => 'calendar',
@@ -1653,14 +1645,14 @@ class Contacts extends Contacts\Storage
 							$link['extra_title'] = $link['title'];
 							$link['title'] = date($GLOBALS['egw_info']['user']['preferences']['common']['dateformat'],$event['start']);
 						}
-						$calendars[$id]['last_link'] = $link;
+						$calendars[$uid]['last_link'] = $link;
 					}
 				}
 				else	// future event --> check for next event
 				{
-					if (!isset($calendars[$id]['next_event']) || $event['start'] < $calendars[$id]['next_event'])
+					if (!isset($calendars[$uid]['next_event']) || $event['start'] < $calendars[$uid]['next_event'])
 					{
-						$calendars[$id]['next_event'] = $event['start'];
+						$calendars[$uid]['next_event'] = $event['start'];
 						$link = array(
 							'id' => $event['id'],
 							'app' => 'calendar',
@@ -1674,7 +1666,7 @@ class Contacts extends Contacts\Storage
 							$link['extra_title'] = $link['title'];
 							$link['title'] = date($GLOBALS['egw_info']['user']['preferences']['common']['dateformat'],$event['start']);
 						}
-						$calendars[$id]['next_link'] = $link;
+						$calendars[$uid]['next_link'] = $link;
 					}
 				}
 			}