iTunes 10.4 makes album art "doubled."
As you can see the image above, iTunes duplicates the same album art by itself.
I simply put an album art to the files that doesn't have any other album art.
However, after I added the image, I found that the music files now have 2 same images.
It doesn't mean iTunes 10.4 duplicates album arts of the entire libary because this behavior does not apply to the files that were album-arted on previous version of iTunes.
It happens to the newly album-arted files on iTunes 10.4.
However, a funny thing is, this behavior doesn't seem to happen to every file.
See the image below. This file which I album-arted on iTunes 10.4 has only one album art.
I'm confused.
I originally thought this only happens to AAC files because John Mayer's "Room for Squares(the second image)" is MP3 while "Heavier Things(the first image)" is AAC but I was wrong because "Battle Studies(the third image below)" is MP3 too but has 2 images while Jeff Beck's "Blow by Blow" which has only one image is AAC so I concluded that weather it's MP3 or AAC doesn't result in this issue.
The next logic I come up with was that it's an image.
I suspected the image has something and that is why iTunes 10.4 duplicates it.
Hint? I was wrong again.
I tried putting the same image to multiple albums and the result was equivocal.
So, it is not music files, and not images either. Then what? It's METHOD.
The method I put album arts accounted for this multiple results.
Method 1: You can just drag and drop an image to the iTunes windows. (see below)
Method 2: or you can open "Get Info" window and double-click "album art" and it opens finder and you choose the image. (See below)
The method 2 results in this duplicate bug. Method 1 is fine.
While I found a workaround, I still don't understand this behavior.
iHope iTunes 10.4.1 would fix this bug.
iMac, Mac OS X (10.7)