So i\'m building a small application, it uses core data database of ~25mb size with 4 entities. It\'s for bus timetables.
In one table named \"Stop\" there are ~130
This may be late for you, but may help others.
I had the same problem. What I found is that, if persistant store type is NSSQLiteStoreType the returnDistinctResults works. But for NSXMLStoreType distinct values are not working.
I haven't tested results for NSBinaryStoreType and NSInMemoryStoreType.