For the last few days I've noticed Mezzmo.EXE (version 3.0.2.0) is using about 50% (1 whole core) of my machine's CPU. In the status window it shows that it's processing active playlists with 5850 file remaining. The number of files never seems to increase or decrease. A quick look in Process Explorer shows that it's in this thread:
Mezzmo.exe!CPlaylistParserManager::GetPlaylistPars er+0x1f3093

I've only got one custom playlist. It's a dynamic playlist that lists videos in the folder tree.