I'm trying to merge http://musicbrainz.org/release/7979007e-1806-4df4-be7a-c3413b74786f (release A) and http://musicbrainz.org/release/acd4fd1b-c3d6-4b69-a82d-cd68d45d1cd5 (release B); disc 2 in A should become disc 3, and the only disc in B should become disc 2 (context: Edit #15400629).

Steps I'm following:

• Select both releases for merging
• Choose to merge into the first release, with Append strategy
• Renumber disc 2 in A as disc 3 (the B disc is already shown as disc 2)
• Try to enter edit

The editor does not let me enter the edit, and shows a "This merge strategy is not applicable to the releases you have selected" message. But if I leave the discs in A as 1 and 2 and renumber the B one to 3, then the edit is allowed (Edit #15400671).