diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index f6079db1..b67d84c9 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -1185,8 +1185,8 @@ class calendar extends rcube_plugin
       $_savemode = $event['_savemode'];
 
       // send notification for the main event when savemode is 'all'
-      if ($action != 'remove' && $_savemode == 'all' && $old['recurrence_id']) {
-        $event['id'] = $old['recurrence_id'];
+      if ($action != 'remove' && $_savemode == 'all' && ($event['recurrence_id'] || $old['recurrence_id'] || ($old && $old['id'] != $event['id']))) {
+        $event['id'] = $event['recurrence_id'] ?: ($old['recurrence_id'] ?: $old['id']);
         $event = $this->driver->get_event($event);
         unset($event['_instance'], $event['recurrence_date']);
       }
diff --git a/plugins/libkolab/lib/kolab_format_xcal.php b/plugins/libkolab/lib/kolab_format_xcal.php
index 4d3a7583..3a9ad1f6 100644
--- a/plugins/libkolab/lib/kolab_format_xcal.php
+++ b/plugins/libkolab/lib/kolab_format_xcal.php
@@ -662,10 +662,17 @@ abstract class kolab_format_xcal extends kolab_format
                 $b = $b->format('Y-m-d');
             }
             if ($prop == 'recurrence' && is_array($a) && is_array($b)) {
-                unset($a['EXCEPTIONS']);
-                unset($b['EXCEPTIONS']);
+                unset($a['EXCEPTIONS'], $b['EXCEPTIONS']);
                 $a = array_filter($a);
                 $b = array_filter($b);
+
+                // advanced rrule comparison: no rescheduling if series was shortened
+                if ($a['COUNT'] && $b['COUNT'] && $b['COUNT'] < $a['COUNT']) {
+                  unset($a['COUNT'], $b['COUNT']);
+                }
+                else if ($a['UNTIL'] && $b['UNTIL'] && $b['UNTIL'] < $a['UNTIL']) {
+                  unset($a['UNTIL'], $b['UNTIL']);
+                }
             }
             if ($a != $b) {
                 $reschedule = true;