diff -urN ../xcalendar.orig/program/EventBase.php ./program/EventBase.php
--- ../xcalendar.orig/program/EventBase.php	2020-12-23 17:57:19.000000000 +0200
+++ ./program/EventBase.php	2021-03-24 20:51:48.308598000 +0200
@@ -1589,7 +1589,8 @@
                 $comment = trim($attendee['comment']);
 
                 if ($comment) {
-                    $comment = ";X-RESPONSE-COMMENT:\"".
+//                     $comment = ";X-RESPONSE-COMMENT:\"".
+                     $comment = ";X-RESPONSE-COMMENT=\"".
                         htmlspecialchars($attendee['comment'], ENT_QUOTES, "UTF-8", false) . "\"";
                 }