How to create smart playlists on iPhone?
Either you have on your library same album and different artists or, most likely, you're creating some weird rules that generate that behavior, like other folks did. If that's the case, seems like you'd have to change + to ... in any rule that uses the plus sign. Granted, it is inconsistent behavior in this second case and it might get fixed in the future. And, who knows, there might be few other little bugs like this as well.