Tracks appearing in ‘groups’ they don’t belong to

[simoncn]

WAV files use ID3v2 tags. These tags can contain a frame named POPM (popularimeter) which includes a rating value. Until recently, MinimServer ignored the POPM frame. From update 125 onwards, MinimServer reads the POPM frame and maps the rating value in this frame to a RATING tag.

From what you have described, it sounds like some of your WAV files contain ID3v2 POPM frames and MinimServer is mapping these frames to RATING tags that you don't want. The fix is either to remove POPM frames from your WAV files or (as you have done) change from using the RATING tag to some other tag name.