MP3 song information not retained after iTunes 7.0 - ID3 tags at fault?

Question

I'm having some strange problems with track information in iTunes. I first noticed it when I tried to copy some mp3's from my Mac to my mobile phone: certain tracks did not retain the song information, like artist, album etc., while others did.
A similar problem has been discussed in this post:
http://discussions.apple.com/thread.jspa?messageID=3698498
However, my problem seems to be a little bit more specific.
If I look at the music in my library in iTunes, all the track information is there. However, for MP3's encoded after 16th October last year, the "Imported With" field, using Get Info, is shown as "Unknown". Before this date, it is shown as "iTunes v7.0". For all MP3's the ID3 version is v2.2.
I believe that I must have upgraded to iTunes 7.0.1 around this time, since I have a number of Apple Lossless audio files which have also been imported and don't show this problem.
The main problem is with the file ID3 tag information (I think). If I select one of the problem tracks, find the original file, open it up in Quicktime and "Get Info", no track/album/artist/composer information is displayed. This is NOT true for 1) MP3's encoded before 16th October 2006 and 2) Apple Lossless files encoded at any time.
In other words, the track information for songs encoded with iTunes 7.0.1 and later is either encoded in a way that no other application can read, OR is only being stored in the iTunes playlist, NOT the file itself. I can see all the track information for these problem files on my iPod, but NOT my mobile phone (where I have to manually copy them over), even if I drag and drop them directly from iTunes.
I have this problem with Quicktime, my mobile phone music player and RealPlayer, so I'm assuming it's "system wide". It even occurs if I copy a problem file out of my music folder and onto the the Desktop, then manually add the track to iTunes: all the song information has disappeared.
I have all my music stored on an external hard disk - 160GB Freecom ToughDrive formatted as HFS+. Previously it was stored on an external disk formatted as FAT32, but copying the files over to the new disk didn't change the problem.
I considered using the "convert ID3 tags" option to see if it would make a difference, but both the good and bad files are listed as using v2.2. I also don't understand enough about them to feel confident converting them to something different - perhaps to v2.3 or v2.4 - just to see if it makes a difference.
Any information on how to "recover" the missing information (for anything other than iTunes) would be greatly appreciated!
MacBook Pro 17" 2.16 GHz 2GB RAM   Mac OS X (10.4.9)   iTunes 7.1.1

Answer 1

Okay, some more information as I try and track down the source of the problem.
By using an id3 tag editing program - ID3 Editor - I was able to view the song information for each track, even though all the other music players I had tried would not show it. If I then chose to modify and update the ID3 information, this would somehow modify the tags in such a way that they become readable in all other programs.
I tried using the "Convert ID3" tags option in iTunes, just on a whim, but without any success. Saving the song information in ID3 Editor doesn't change the version of the ID3 tag - it's still listed as v2.2 in iTunes - but it DOES make it readable in other programs. I also tried the various text conversion options, again without any success.
This looks to me like a bug in iTunes. While its possible for me to get around it, in an extremely long winded way, I still can't understand why iTunes would be writing ID3 information that other Apple programs cannot read.
Any suggestions? Should I be posting this question in a different forum perhaps?