I guess since the most recent server update, it now appears to be impossible to edit 8cm CD releases if they have attached disc IDs.
Take this release for example (although every 8cm release I tried seems affected), select "Edit", then make no (or any) change whatsoever. Go to "Edit Note" tab and you see
Some errors were detected in the data you’ve entered. Click on the tabs shaded red and correct any visible errors.
The tracklist tab is shaded red. If I go there:
Format: 8cm CD
This medium has a disc ID, pregap track, or data track, so you can only change the format to one that can have disc IDs.
The error goes away if I select just "CD" in the format dropdown, but that's not correct for this release, so...
It seems like all the various CD subtypes are busted in this manner.