It would be far more intuitive for new users, and result in better data quality, if when adding a new release you were prompted to specify the number of discs before adding any tracks.
Currently, you have to know that for multi-disc releases you enter only the first disc's tracks, then click "add release", get presented with a poorly labelled box, and then somehow add disc 2's tracks (again?), then repeat for subsequent discs.
Far better would be:
1. Enter number of discs this release has.
2. Click OK/Add (or other suitably labelled button)
Then either the current system, or even better:
3. A list with that number of entries appears, asking for the title of each disc (if any) and the number of tracks on that disc
4. Click OK/Add (or other suitably labelled button)
5. The tracklist entry screen appears, pre-populated with the given number of tracks for each disc
My reasoning for all this is that it follows the intuitive process of setting the structure first, starting with the major divisions (discs), then the minor divisions (tracks), before entering the details.
When entering a new 3-CD release, I saw it prompt for the number of tracks, so I added the 60 tracks of the release, assuming I could allocate them to discs somehow later. When I did find the "add disc" button it seemed to be asking to import tracks from somewhere else or in a free-form text field so I figured that it wasn't what I was looking for.