I had imported a bunch of mp3's from my itunes library into my LMCE machine and noticed that some songs were missing from the audio database. Or rather their id3 metadata was missing, so they were not showing up when filtered for anything other than file. LMCE was somehow not recognizing the ID3 tags.
To make a long story short, after much hair pulling and experimenting I noticed that only ID3 tags which were Version 2.3 were being recognized. V2.2 and 2.4 seemed to be simply ignored.
I am not sure if this is a glitch or intentional but figured the discovery could help others who have had music seem to disappear...