Hi Will,
If you want to know if a problem has been reported before, the place to start is the ticket tracker: here's a search of all tickets that mention urlize:
From a quick scan, I can't spot anything related to ellipses; there's a recent ticket related to exclamation marks, though:
which would suggest that there is a known subclass of punctuation-related issues. If you've got a case that reliably breaks (which it sounds like you do), open a ticket describing the exact problem, and if you're really adventurous, try your hand at a patch and pull request. The full guidelines for contributing can be found here:
Yours,
Russ Magee %-)