If you are trying to filter using a keyword that carries a punctuation you might experience problems with the RSS filter of FilterMyRSS.  So for example, lets say you have an entertainment blog and want to filter celebrities who “can’t sing” then running a feed filter from FilterMyRSS might show incorrect results.

It is best to use the keyword filter “cant sing” for the filtered feed as nearly all permalinks exclude the apostrophe in the permalink structure.