In case anyone else hits this, I 'solved' it by setting a merge policy on the
managed object context:
[_managedObjectContext setMergePolicy:[[NSMergePolicy alloc]
initWithMergeType:NSMergeByPropertyObjectTrumpMergePolicyType]];
This very much feels like a workaround. According to the document
Dear list,
I have two different core data apps, both of which are exhibiting similar
behaviour in that they sometimes (for some changes in some properties) can’t
save the MOC. Here is an example error I get when using
[moc save:error]
Error Domain=NSCocoaErrorDomain Code=133020 "Could not merg
