Again I struggled about how to merge releases using "Merge mediums and recordings".
To avoid wrong edits, the "Merge releases" page should give more information about how the merge works, esp. how disks with matching number of tracks are handled.
Proposed text (if this is correct):
When merging releases with different number of disks, make sure all media are in the correct position. This can be done using the up- and down-arrows in the tracklist editor.
Maybe more information is helpful.