Please ignore if fixed, but I'm using mp3val-0.1.8_with_frontend-0.1.1-bin-win32 and it has this issue.
Tracks are not loaded from a folder, if the .mp3 extension is in a different case (i.e. .Mp3 or .MP3).
Frustratingly, it took me a while to realise this, as most of my files are correctly named.
Some kind of reporting at least, is warranted, or recursive is not trustworthy.
Thanks for the excellent program otherwise, and hope you still intend to release an update.