The plugin's forum is down... :(
Here is the issue: Using the UTW plugin I've tried to add a "compund" word and a single word as one tag, e.g. word-press question.
In the URL (when clicking on the tag) it displays correctly; however in the tag list the dash [-] is stripped. That wouldn't be a big tragedy... but if you choose to display the Wikipedia icon, the link structure will be built from the 'displayed' form, i.e.
This sucks, since I know for sure there IS a "/word-press_question" type wikipedia page - but my tag doesn't go there, it looks for /word_press_question, which doesn't exist.
(the example is fictional, of course)