unflagged emails stays in flagged folder

When I unflag some emails that I had previously flagged for follow up, they stay in the flagged email folder even though the flag is gone. Here are the bandaids that I have been using.

Bandaid 1 - Rebuild the email folder. It does work and gets rid of the rouge emails in the flagged folder, but within a few days a few other previously flagged emails exhibit the same behavior. Daily rebuilding emails is not a permanent solution.

Bandaid 2 - deleting the rouge emails and then un-doing the delete sometimes (but not always) takes them out of the flagged folder.

Bandaid 3 - right clicking on the rouge email and moving it to it's original inbox (which it shows it's already in), will almost always cause it to disappear from the flagged folder.

But these are all a pain! Mac Mail shouldn't be doing this. Does anyone know a permanent solution to fix this? How does one report a bug to Apple developers?