Not sure if its just me, but in version 1.4b of Limewire, for example, I have a directory with a album of songs in mp3 format... I also have in this same directory the same songs in WMA format.

The problem is that Limewire will only display one version of the song (wma or mp3), it won't list both. I assume because their name is the same (even though the extension is different).