Forward Slashes in ID3 TXXX tags

I have some existing Musicbrainz ID3 tags on mp3 files. For example, a TXXX frame for the musicbrainz album type, and it contains the text “album/compilation”. I’m finding that when imported beets rewrites these tags with the text: “[/‘/a/l/b/u/m/’/,/ /‘/c/o/m/p/i/l/a/t/i/o/n/’/]”

Can someone tell me why? Is this a separator issue? Does beets not handle the forward slash correctly?