FLAC tags are working properly for me (i.e. displayed in playlist and info inspector but not in file tree view). Which build are you using? Could you upload somewhere an example of FLAC for which tags aren't working for you?
It definitely wasn't related to FLAC issue, i'd need those FLAC to investigate.
you're right, i'm really sorry! flac tags are recognised, though i don't see any artwork. but this might also be a problem with the tagging software (i use tag 1.0b by sbooth). there was a time when i saved my music as .aac, and those tags really aren't recognised, but i guess they aren't supposed to be? seeing that .m4a files work.. (i'm really no expert with file format and metadata format stuff)
actually, it seems to me like only artwork in files with id3 is shown...
Oops, haven't been getting notifications on comments here.
Will have a look at metadata handling for aac - might be a bug.
As for artwork, is it embedded inside flac/m4a/aac? If so - can you upload and example somewhere? I don't have any of those locally.