diff --git a/plugins/libcalendaring/lib/libcalendaring_itip.php b/plugins/libcalendaring/lib/libcalendaring_itip.php
index 2e122c2a..93e33a62 100644
--- a/plugins/libcalendaring/lib/libcalendaring_itip.php
+++ b/plugins/libcalendaring/lib/libcalendaring_itip.php
@@ -258,8 +258,8 @@ class libcalendaring_itip
 
       // check if the given itip object matches the last state
       if ($existing) {
-        $latest = ($event['sequence'] && $existing['sequence'] == $event['sequence']) ||
-                  (!$event['sequence'] && $existing['changed'] && $existing['changed'] >= $event['changed']);
+        $latest = (isset($event['sequence']) && $existing['sequence'] == $event['sequence']) ||
+                  (!isset($event['sequence']) && $existing['changed'] && $existing['changed'] >= $event['changed']);
       }
 
       // determine action for REQUEST
@@ -320,7 +320,7 @@ class libcalendaring_itip
                     )
                 )));
               }
-              $action = $attendee['status'] == $status ? '' : 'update';
+              $action = $attendee['status'] == $status || !$latest ? '' : 'update';
               $listed = true;
               break;
             }
diff --git a/plugins/libcalendaring/libvcalendar.php b/plugins/libcalendaring/libvcalendar.php
index 4f64dead..855e0749 100644
--- a/plugins/libcalendaring/libvcalendar.php
+++ b/plugins/libcalendaring/libvcalendar.php
@@ -919,7 +919,7 @@ class libvcalendar implements Iterator
         if ($event['description'])
             $ve->add('DESCRIPTION', strtr($event['description'], array("\r\n" => "\n", "\r" => "\n"))); // normalize line endings
 
-        if ($event['sequence'])
+        if (isset($event['sequence']))
             $ve->add('SEQUENCE', $event['sequence']);
 
         if ($event['recurrence'] && !$recurrence_id) {