Ok, I belive this is a bug. It's a small one, but an annoying one. I'll try and explain it as best I can. Here goes. 

Album A is a normal album with just one artist in genre 1.

Album B is a compilation album and has various artists including one track with the artist from album A, however this album is in genre 2.

When browsing genre 2 album B shows up under "Various Artists" as it should, except however the track that shares the artist with album 1. This track shows up outside "Various Artist" as a regular artist. Which is normal had it been genre 1. Since this is another genre it shouldn't show outside "Various Artist" (only in genre 1).

The problem doesn't occur when browsing on the server, but the controller does it wrong as described above. Seems like genre is ignored when an artist from a compilation is grouped with non compilation albums from the same artist.

I use the iTunes plugin, but I don't think it's related.