@wolffang - I got your PM regarding the "change vote" option not working. Maybe Damelon already had fixed the poll, but I checked and there seems to be sometimes a bug for that option when the poll is not created by a local/global moderator with certain permissions.
I applied a fix so the permissions are processed properly, and I just checked with a test user and it does work. So in any case, if anyone wants to undo their votes and vote again, just use the "Remove vote" button right under the poll options.