I recently ran across a somewhat curious problem which I believe is worth pointing out here.
I imported several CD's either as original disc or as flac or mp3 from the net in to iTunes/iPod touch and used the onboard converter to translate mp3 into m4a. This all worked fine and all releases by that particular artist ended up in iTunes under the correct band name.
However, upon synchronizing the iPod, one of the albums was missing under the band name although it was present as an "album". There was no clue within the informations how this could occur. After quite some fiddling around - including rebuilding the data base - I checked with mp3tag for the details of these particular mp3's which had served as source - nothing.
It then turned out that apparently this particular album was tagged as "compilation" and hence treated differently by the iPod touch as compared to iTunes. Well, no commentary required, I assume.
But I could not get rid of this hidden tag neither by iTunes nor by mp3tag.
I finally resorted to reconverting the files via audacity into wav and concurrently removed all "suspicious" data upon conversion, then reloaded the files into iTunes and reconverted the wav files into m4a.
That did the trick.
Apparently, there are tags in mp3 which can even be carried over into wav and do not show up in mp3tag.