If you search for problems with ID3 tags and iTunes you get a lot of result, and the problems people seem to have varies a lot. I myself have had problems for years and never figured it out before, but recently I got so annoyed and really wanted to get to the bottom if the issues I had.
One problem that many experience seems to be that you update your ID3-tags from within iTunes and you put a lot of effort into keeping you music collection organized, and then for some reason when you play your song a couple of months later the incorrect id3-information that you removed is suddenly back!
There are two different major versions of ID3; ID3v1 and ID3v2. And mp3 files can have both at the same time because some devices can't read ID3v2 and then they will fall back to ID3v1. The problem is that iTunes does not update the ID3v1 tag.
I filed a bug in Apple Bug Reporter with ID 11432980 in May. No response yet...
As long as you stick to iTunes you are good, but if you let other applications "touch" your music you are in trouble. Or to put it more correct, as long as you stick to iTunes, you won't see the problem.
I use Traktor for DJ:ing and sometimes other applications to do stuff with my music. When I play songs in Traktor the songs gets analyzed for bpm etc, and the bpm field in the ID3 tag is updated by Traktor. When back in iTunes and I play the song again iTunes can see that the song has been "touched" and will read in the ID3 information from the file. And this is where you notice the problem, because iTunes then reads from both ID3v1 and ID3v2. So if you removed the album name from within iTunes then it only got removed from the ID3v2 tag, and when iTunes reads the information again it merges the ID3v1 and ID3v2 information and all the time you have put in organizing your collection is lost!
My solution to the problem until Apple fixes the "bug", is that I have removed the ID3v1 tag completely. There are different ways and different applications to do this but I found ID3 Editor by Pa-software (ID3 Editor - the small and simple MP3 tag editor) to work very well in my case. You can manually open the song in ID3 Editor from within iTunes using the bundled applescript from PA-software called "Edit selected tracks in ID3 Editor". What makes ID3 Editor stand out from the other applications I have tried is that you also get a command line interface that works great. The usage is as easy as "id3edcmd -rm1 /path/to/song.mp3" to remove the ID3v1 tag, and you can use this in any solution you prefer. I have modified their bundled applescript to execute this command instead of opening the file. So I execute this script on all songs I import and my problems are gone
The script from Pa-software is copyrighted and I don't think I can post it here but I can post the part I wrote so you can use it yourself. You will of course need the ID3 Editor installed on your computer. I think they have a trial version but otherwise its only $15.
repeat with this_track in these_tracks
set this_name to the name of this_track
set this_location to the location of this_track
set this_location_posix to POSIX path of this_location
set this_location_posix_quoted to quoted form of this_location_posix
set command_line_action to the "/usr/local/bin/id3edcmd -rm1 " & this_location_posix_quoted
do shell script command_line_action
end repeat
And another trick for Traktor users is to don't let iTunes "Keep iTunes Media folder organized", because then iTunes will move your files if the ID3 information is updated, which causes problems if you have applications like Traktor that have references to songs in your iTunes Media folder. I only use the "Copy files to iTunes Media folder when adding to library".
