I posted this under a different issue before http://ktorrent.org/forum/viewtopic.php?f=1&t=2749 but thought it needs it's own post since it still seems to be around.

If you have more then 2 RSS Feeds setup, and you have a filter applied to both of them, and each of them have a torrent for the same season/episode, it will download both.

Screenshots attached.
String Matching is: ^(?=.*\bThe.*Mentalist.*HDTV\b)((?!x264|720).)*$

This bug was also present in 3.2.4. It is the only thing keeping me from using kTorrent