1) the widget
The fbcalendar ics url has a comma in it. The widget tries to allow for combining multiple urls, separated by commas - that is why that is a problem - it thinks the one url is 2 separate urls. You "fixed" the url problem by passing it through google, which gave a friendlier URL.
In the long run, I will probably change the widget to allow one to use the same entry as in the shortcode (it would have to override whatever else one had entered in the widget fields, just as the shortcode overrides the admin settings). This would avoid the comma problem.
Note: By passing the url through google, you are actually changing the event datetime definitions. See http://icalevents.anmari.com/2064-ical-local-or-floating-date-times/. This partly explains the "difference" in times you saw initially.
2) Times & Timezones.
The fbcalendar is issuing local "floating" times: DTSTART:20100202T161500
The spec says that these will always be in the "attendees" timezone. See also http://icalevents.anmari.com/1634-artistdata-ical/.
The plugin is supposed to implement these as being that time no matter what timezone is specified.
However google changed the way the dates were specified. So in the widget it basically created these in the UTC tz and then converted them to Oslo time. This resulted in the correct behaviour due to the way google spec'ed the event:
DTSTART:20100202T151500Z with overall calendar being in oslo time.
In one of the last couple of updates I added a piece of code which I should not have, which has caused a bug in local times (it creates them in UTC, when it should create them in the wordpress install timezone). I guess you forced the shortcode to tz=UTC to get the fbcalendar to give correct times.
The widget does not have the ability yet to force a timezone - like the shortcode does. It has to use the tz from the wordpress install.
Luckily for you when I fix the local time creation, your times should be okay. However if/when you make changes, please note these differences in files.