I don't know if it is a good place to post this question. But as Microsoft doesn't have any jira or other bug tracker I'm posting it here.
The problem has to do with albums sorting on Windows phone platform.
If two files have one album's name but different artists they are considered as different albums.
For example check it out what I have in my library.
If Microsoft is afraid that albums with the same name but with different(really different) artists will be considered as one, they can take into account their location. If they are in one dirrectory it means that that this files belong to the same artist. Or they can use other tags.
I believe it's a very common problem... All music players that I found in wp market have this problem, because they use the standart API.
Pls don't say that I have to edit tags before uploading to my phone...
I hope I don't have to write my own player to fix this bug.