Issue/2596 fixes coredata threading glitch

Fixes #2596

> would hide the real problem, which is... posting a notification in a BG thread

I don't mind if this is the approach we take, but that's not the problem. There's nothing wrong with posting and receiving notifications in background threads. It's UIKit who wants to do everything in the main thread; the UI code should be responsible for ensuring it's on the right thread. A class in the data layer posting a notification in the background sounds perfectly acceptable to me.

Anyway, it's probably OK, even if just for consistency (IMO, we're doing notifications wrong everywhere) ;)