[horde] ActiveSync -> CalDAV Timezone quirk

[Steffen]

Hi,

with
Horde_ActiveSync             2.31.6  stable
kronolith                    4.2.15  stable

when I create an event with Android ActiveSync, I get an entry with 
event_timezone = 'CET' in the database; the GUI and ActiveSync display the 
event correctly. But when downloaded by CalDAV I get this:

BEGIN:VCALENDAR
VERSION:2.0
X-WR-CALNAME:Calendar of dvtest1
PRODID:-//The Horde Project//Horde iCalendar Library//EN
BEGIN:VEVENT
DTSTART;TZID=CET:20160308T150000
DTEND;TZID=CET:20160308T153000
DTSTAMP:20160314T123714Z
UID:20160314132443.4C_Xp8mUFWBF6GsNZi0nVRb at ...
CREATED:20160314T122443Z
LAST-MODIFIED:20160314T122443Z
SUMMARY:B15:00
CLASS:PUBLIC
STATUS:CONFIRMED
TRANSP:OPAQUE
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:B15:00
TRIGGER;VALUE=DURATION:-PT15M
END:VALARM
END:VEVENT
BEGIN:VTIMEZONE
TZID:CET
END:VTIMEZONE
END:VCALENDAR

My client is totally confused by the timezone CET. If I replace the string 
CET by "Europe/Berlin" in the database, I get the correct date in the 
CalDAV client, too, and a lot more entries in VTIMEZONE.

The user has Europe/Berlin as default timezone, as does PHP.

Is this some configuration error?
If I remember correctly, ActiveSync storred UTC as timezone, didn't it?

-- 
Steffen