Steps to reproduce

• Go to submit toc
  http://test.musicbrainz.org/cdtoc/attach?toc=1+15+286355+150+13219+33253+53265+72283+88532+105368+125113+143641+161137+180391+198135+213775+234166+255308&filter-release.query=Broken
• For test purposes, add it as a new release
• Set artist to Nine Inch Nails (test purposes)
• Go release duplicates. Pick any release; i chose the 8-track
• Click next
  >> DiscID/TOC is lost at this point (see edit notes, there is no "Add disc ID" edit)

This also happens if you choose a release with the same number of tracks.

The expected behaviour here is probably complicated. Since there is a TOC being attached, the track times etc in the "based on" release cannot be used. However if I'm adding a release with bonus tracks, I think I'd expect to be able to re-use the titles and have the editor discard the times. Being able to copy titles/artists is the safest way so that the tracklists can be shared using the "matching magic" in the database, I believe?

I think in this situation it should give you a warning.

I'd suggest something like the following on the release duplicates page; suitably highlighted:

"You are adding a DiscId with this release. If you base this addition on an existing release, the track times from the existing release will be ignored"

If existing release # tracks < discID # tracks => empty titles tracks should appear in tracklist editor
If existing release # tracks > discId # tracks => should pick the first "disc # tracks" and populate those in tracklist. Perhaps it should give you a warning that it has discarded some track titles.

But you should not lose the TOC/discId without any warning, which is what is currently happening.