Same coverart in mp3

I understand now why command "SetAttr META coverart" something "failed" when I try to delete coverart in mp3 file.

Copy jpg file to clipboard, open metapane and paste it 5 times with Paste button. 5 thumbnails are display in metapane.
After applying changes, only 1 thumbnail, so you can imagine that duplicates are not added and mp3 has only 1 coverart.

Now, you want to delete coverart. So you can over thumbnail in metapane then click Delete then Apply or use command "SetAttr META coverart".
But "Oh surprise!", coverart is always here.
You need to delete 4 times again to delete coverart completely.
10 (143 KB)

Other thing with cover art...
This mp3 file has cover art but not display in metapane. Cover art is display in thumbnail/infotip.
By script, you can see that this file has 3 cover art.
3 coverart not display in (716 KB)

No news about this ?

Whatever stored those coverart images has marked them as image/jpeg but they're actually in PNG format.