Firefly’s logic, for now, is to populate WMA’s Album Artist metadata into Artist if it doesn’t exist. The Album Artist is actually shoved into what Ron calls Orchestra in his database… probably because that’s where he puts MP3 ID3v2 TPE2 (aka Band, aka Album Artist — well, as close as you can get)
On the flip side, if there is no “Album Artist” in the WMA… Orchestra gets populated with Artist.