Moved from http://bugs.musicbrainz.org/ticket/5167
If an MP3 file contains multiple cover images, Picard removes all but the last one. This is best illustrated using NIN's albums offered for free download (Ghosts I and The Slip): each track contains its own artwork, while the first track has two pieces - one cover for the whole album, and artwork for the first track itself. After saving the tags in Picard, the album cover is gone, leaving only the track cover.
Steps to reproduce
1. Store two covers in the MP3 file using compatible tagger (I used iTunes and Mp3tag).
2. Open the file in Picard.
3. Save tags.
All cover images are preserved.
The first cover is removed.
Still happens in 1.1.