This has to be my favorite topic! I have finally identified why the ical feed is not fully compliant with many ical subscription services.
1. X-WR-TIMEZONE non-standard advisory timezone property.
2. The iCal feed uses 'floating' time for the events and not VTIMEZONE
This is a bug in the iCal feed. A fix would be to use an iCal feed
that either does not use X-WR-TIMEZONE and/or uses non-floating time.