We used to have this problem with IE6. It is caused by browsers mangling encoding data. It happens when the browser can't properly handle UTF8 for some reason.

Can you let us know what browser you're using and - ideally - the specific words that are causing problems and how they got into your vocabulary list (did you "click to add" somewhere, or were they imported manually?). If we can replicate the problem we can look for ways to fix it, or at least catch "garbage" entries from creeping into your list.

In the meantime, a manual way to remove these problematic entries is to visit your vocabulary list and delete them manually:

http://popupchinese.com/vocabulary

NOTE: I've just removed the problematic entries from both your and Breezy's account.