Fetched Properties

Remember, when you are using fetched properties, they will not automatically be updated if the things they are referencing change. They should be seen as static values that need to be updated manually. Which is pretty easily done by...

[_managedObjectContext refreshObject:object mergeUpdates:YES]

This is something that always ends up biting me at some point until I re-read the CoreData programming guide (which I always seem to be doing)