Unwanted hollow star / album ratings foul up a Smart Playlist of zero-star songs
You can get rid of album ratings. Select "as album list" from the view menu, then click just to the left of the leftmost star. This will clear the rating, although you may have to try a couple times to hit the right spot, especially if you have 1/2 stars enabled. 

Source:

https://discussions.apple.com/thread/1786573?threadID=1786573