WMP Artist fields - update 2
A further update to that article:
If the Album Artist field is empty, WMP will create a node in that (Album Artist) tree, based on the first listed Contributing Artist (if that field is not empty).
One of the consequences of this, is that if you have a bunch of tracks that are listed under an Album Artist node "Foo 1"and some of them are there because their Contributing Artist field is blank, then you drag them all to another Album Artist node "Foo 2", then some will have their Album Artist field change, and some will have their Contributing Artist field changed. Of course, WMP only asks for confirmation of a change of Artist field. And an unqualified Artist field can mean almost anything in WMP...