The fetch requests created inside RKManagedObjectDeletionOperation's main method are missing an init call.
The following source code line in RKManagedObjectDeletionOperation.m should be changed from:
NSFetchRequest *fetchRequest = [NSFetchRequest alloc];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
I noticed this when I observed that some of my subentities were't correctly deleted by my deletion predicates (due to includesSubentities not being set to the default value of YES).