If the user has configured Picard to download only images of type X (e.g. 'front'), and an image on CAA is tagged as both X and Y (e.g. 'front' and 'booklet'), then the album is shown as 'modified' after a look-up. If the 'new' data are then saved, the album will again show as 'modified' next time it is looked up.
I think Picard should ignore image tags from CAA that correspond to types that the user has chosen not to download.
Suggested fix: in CoverArtImage._init_ in image.py, change:
Works for me.