Does anyone still have this bug?
I recently updated from 3.4.8033 to 3.5.8150 and discovered the new feature and have this display error.
I also noticed the opposite, when I right-click a song > "include in playlist", sometime the playlist is unticked even though the song is in the playlist (and if I click it I have the popup saying "Duplicate track detected - do you want to add the track to this playlist?").
The new feature is kind of unpractical for me until it's fixed, but I think it's a really good idea and would love to see it work as expected!
Edit: Sorry just realised the version of musicbee I have isn't the one supposed to have the fix (I thought I skipped a few updates and the bug was already supposed to be fixed in 3.5.8150).
Looking forward for the next version!