yeah, itunes did something similar to me... I had doubles of a bunch of songs and for some reason it stripped out the name of the artist for each track. The artist\'s names show up fine if I play my music in itunes, but the actual file names in windows explorer or on my zen is the track number and song title.
A minor annoyance... going through about the 200 or so songs that were affected and manually adding the artist again through the id3 tag