Merging Multi-Disc Albums

[gemi]

I have the following problem merging multi-disc albums:
- All tracks in all discs have the same ALBUM tag
- All tracks in all discs have the same ALBUMARTIST tag. However it is a list instead of a single value.
- Most tracks have the same ARTIST tag. This is also a list.
- One disc has tracks with a different ARTIST tag.

Now, the album is split on the different ARTIST tag.
If the ALBUMARTIST tag is a single value, instead of a list, everything works as expected.

It seems that ALBUMARTIST being a list causes the problem.