Released versions up to Amarok 2.7 treated MusizBrainz id embedded in tags (filled in by MusicBrainz-enabled tagger such as Picard) as unique identifiers of tracks. However, MusicBrainz changed the semantics of the id to mean "recording id" since it was originally implemented in Amarok, which means that you may get false duplicates for example for tracks that appear on the original album and the Best of one. See bug #315329 for more info
