This is a pretty frustrating scenario. When imported to NGS, any release event that didn't specify a format inherited all the DiscIDs attached to the release, regardless of release date. Now in NGS, when a user tries to edit a release that previously had no medium attached to it, certain edits are blocked if a DiscID is attached. (The most annoying one is not being able to assign a medium other than CD to the release; other blocked edits include changing track times or adding/removing tracks, both errors I've run into when trying to change the artist for a specific track).

Before these edits are allowed, the DiscIDs have to be removed, which sucks for two reasons:
1) You have to wait for the votes to finish before you can continue editing.
2) If there wasn't a release event for a CD issue previously, removing the DiscIDs will probably sever any link between that release and those IDs (especially if the the pre-NGS release had no release events, or just one for the original release).

I'm writing a Feature Request to address the second issue. For the first one, it seems like removing a DiscID from a release that doesn't already have its medium set to CD should be an auto-edit, as long as there are other releases still attached to that DiscID.
OR
Instead of being blocked from assigning a medium, users should be asked if they want to remove the DiscIDs as part of the edit. That way, they'd still be subject to a vote.