UNSOLVED Problem with exdate exeption in .ics file

[azuettel]

I have a problem with my .ics file for the standard calendar module. The exeptions “exdate” of an event are stored in the wrong format, it look like this:

BEGIN:VEVENT
DTSTAMP:20181120T052855Z
CLASS:PUBLIC
CREATED:20181120T052855Z
DESCRIPTION:
DTEND;TZID=Europe/Zurich:20170828T082000
DTSTART;TZID=Europe/Zurich:20170828T075000
EXDATE:20170925T055000Z,20171002T055000Z,20171009T055000Z,20171016T055000
 Z,20171023T055000Z
LAST-MODIFIED:20181120T052855Z
RRULE:FREQ=WEEKLY;UNTIL=20171112T065000Z;BYDAY=MO
SEQUENCE:0
SUMMARY:xxx
TRANSP:OPAQUE
UID:2b8ae706-c70f-4592-a380-6d301b5bb624
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
END:VEVENT

but they should look like this:

BEGIN:VEVENT
DTSTAMP:20181120T052855Z
CLASS:PUBLIC
CREATED:20181120T052855Z
DESCRIPTION:
DTEND;TZID=Europe/Zurich:20170828T082000
DTSTART;TZID=Europe/Zurich:20170828T075000
EXDATE:20170925T055000Z
EXDATE:20171002T055000Z
EXDATE:20171009T055000Z
EXDATE:20171016T055000Z
EXDATE:20171023T055000Z
LAST-MODIFIED:20181120T052855Z
RRULE:FREQ=WEEKLY;UNTIL=20171112T065000Z;BYDAY=MO
SEQUENCE:0
SUMMARY:xxx
TRANSP:OPAQUE
UID:2b8ae706-c70f-4592-a380-6d301b5bb624
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
END:VEVENT

Since these are wrong, none of the calendar elements are shown. Any suggestions how to change that?