I'll assume you are talking about version v1.0.x, tell me if you are not.
Thanks for reporting this, I'm no longer working on v1.0.x, and as the way songs data are handled in the new version (v1.0.x currently in alpha) has completely changed, it's unlikely the bug is still there (though there are lots of new ones to play with

).
So unless you can find what action causes this to happen (I doubt it's time, as there is nothing distinguishing an old rating from a new one), I won't be investigating it, sorry.