What type of view are they being grouped in?
I used that album value and it grouped fine under that value in the default "Artists" view for example.
I've attached an image below. I use an expression field, first two columns, the third is the normal album artist field (all three doesn't sort correctly).
As I was writing this, I just noticed that the problems seems to be in the grouping column (other, 1, 2, etc...) in both the expression field and default Album Artist field. If I don't have anything selected there it sorts fine in the non-grouped expression field and default Album Artist field.
It seems like doing a "make that character unaccented" would be pretty reasonable.
I use MusicBrainz for all my tagging (if I find an error in my tags I go to MB to correct it) and sync with there servers a few times a years to update all my tags. I don't alter any tags that MB uses since it will be overwritten upon the next sync. I guess it would be easy enough to add a few lines in the expressions I use to replace the accented characters.