DTSTART;TZID=Europe/Berlin:20130513T080000Z
DTEND;TZID=Europe/Berlin:20130513T090000Z

Here lays you problem.
The TZID says "use timezone Europe/Berlin" but the "Z" character at the end says "This time is in UTC/GMT"
Therefore every client can choose which one he wants to use.

I would suggest fix "Z-time"

Hi,

I just created an event with timezone Europe/Berlin at 8am on Wed using Thunderbird (with the extensions). In thunderbird and on my smartphone, the event is shown correctly at 8am.

In SOGo web interface, it is shown at 6am (using timezone Europe/Berlin there - when using timezone Asia/Dubai, it is shown correctly; but this is no suitable workaround).

The vCalendar code looks like this:

BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/Berlin
X-LIC-LOCATION:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20130603T075813Z
LAST-MODIFIED:20130603T075823Z
DTSTAMP:20130603T075823Z
UID:19b85a0e-0d60-48d3-9cd9-3a1aef806d08
SUMMARY:Test
DTSTART;TZID=Europe/Berlin:20130605T080000
DTEND;TZID=Europe/Berlin:20130605T090000
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR

Best regards,
Freddy

Btw: Same problem with SOGo-nightly

same problem here.

SOGo installed on Debian Squeeze from the apt mirror.

same problem on Ubuntu 13.04 (Raring Ringtail) with precise packages.
Will there be packages for raring anytime soon?

You CANNOT use Ubuntu 13.04 with Precise packages and expect NOT having time shift problems. It won't work, period.

You have to use the packages FOR the distro, otherwise you WILL have timeshift problems.

The solution here is for us to provide packages for 13.04, nothing else.