Oh dang, timing though?! What if this is my invalid bit removal PR? I did say “hopefully no regressions this time” somewhere, I was asking for it 
I did run PR builds, so it might be possible the issues only started with that change. A bit weird people are running in the issue tracker yet if this is it, but then again not that many RC users. I guess I don’t get to call it a day after all and will have a closer look.
Edit: Luckily seems like not: If I pause that one folder, everything works fine. If I ignore a test file, that gets properly ignored. So back to having no clue wtf this is, maybe an edge case, maybe a leftover of a bug from years ago that surfaces now (that syncthing setup/db and file are really ancient).