When wallace is configured to accept invitations and iTip with non-Olson formatted timezone comes to the system, the event start/end time will be converted to UTC without time modification. Example:
BEGIN:VCALENDAR X-LOTUS-CHARSET:UTF-8 VERSION:2.0 PRODID:-//Lotus Development Corporation//NONSGML Notes 9.0.1//EN_S METHOD:REQUEST BEGIN:VTIMEZONE TZID:W. Europe Standard Time BEGIN:STANDARD DTSTART:19501029T020000 TZOFFSETFROM:+0200 TZOFFSETTO:+0100 RRULE:FREQ=YEARLY;BYMINUTE=0;BYHOUR=2;BYDAY=-1SU;BYMONTH=10 END:STANDARD BEGIN:DAYLIGHT DTSTART:19500326T020000 TZOFFSETFROM:+0100 TZOFFSETTO:+0200 RRULE:FREQ=YEARLY;BYMINUTE=0;BYHOUR=2;BYDAY=-1SU;BYMONTH=3 END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT DTSTART;TZID="W. Europe Standard Time":20160831T113000 DTEND;TZID="W. Europe Standard Time":20160831T140000 ...
This does not happen when importing such event in Roundcube, because Sabre libs support windows timezone mapping. This is not the case for pykolab. We should support windows timezones and convert them to Olson-database names.