I just tried out the portable sunbird, great program except for this flaw. When I import iCal from Calendar.Google.com the repeating tasks repeat every day, regardless of the fact that they're setup for weekly events... and not only that it appears to wrap around the year in an infinite loop.
When I look at the "end" date, it shows December 31, 1969.
I downloaded the latest official version just now and the exact same steps work flawlessly. I'm thinking its just a lil bug somewhere.
Also my events have no end time, but even when I added one it didn't seem to make a difference, it just kept on repeating them.
Trahloc
If you copy the latest Sunbird from http://www.mozilla.org/projects/calendar/sunbird/download.html into the \PortableSunbird\Sunbird folder that seems to fix it. Since you still use the PortableSunbird.exe to run it ... guess it must do something outside of itself to make it use the local Profile instead of the system one.
Trahloc
Sunbird 0.3a1 and a2 are alpha releases. Both have known dataloss and crash bugs and are not recommended for production use. As such, you'll run into bugs like this. There's nothing I can do about them since I'm just bundling these test versions so people can try them out.
For day to day use, I recommend Sunbird 0.2 as it is more stable.
Sometimes, the impossible can become possible, if you're awesome!