Once the last tracker from the infowidget list is removed, ktorrent crashes. If it matters, all the trackers in the list were the same.

This should not happen anymore. I fixed that last night.
Make sure you have the latest SVN.

Yep, i can confirm that the fix from yesterday works fine here.

Update and look if you see a small & efficient error notification which says "cannot remove torrent default tracker" when trying to remove the _default_ entries in the trackerlist.
If not, please share.