Thank you for contacting support, the feedback is appreciated! I also want to give a quick thank you to the other users who commented on your post giving suggestions about cleaning up the Library as that would have been my initial suggestion as well.
I would like to see if we can trigger a change in behavior here by asking you to please “disable” (not “remove”) the watched folder that had previously contained the media temporarily. After it has been “disabled”, please relaunch the application, re-enable, and try deleting the mentioned “ghost tracks”.
Looking forward to hearing your observations!