When in the CD TOC view of a release, the column format says always "medium" instead of the actual medium format.
The actual format is however something thats you can see properly in other views like the release group view for example.
ex:
http://musicbrainz.org/cdtoc/q6fO3UBUhki4K9nbBkb56dVdjcg- (says "medium" for all releases)
vs
http://musicbrainz.org/release-group/40a087e8-908a-334d-b520-88a820deb09d (gives mix of CD and other media)