Hi,
I would like to address this issue (http://stackoverflow.com/questions/7385439/exception-thrown-in-nsorderedset-generated-accessors).
The problem is that when I set a one-to-many relationship to be "ordered" in model definition, I receive a runtime exception.
I did not find any topic here related to this issue, so I am creating one here.
As you can see, this issue persists for many years in CoreData.
If you want to complain, you should ensure that you're filing bug reports about the features and posting those bug report numbers in your forum posts. That way you ensure that the engineering teams are seeing your complaints.
Otherwise, as noted in the many answers linked, one work around is provide your own implementations for the methods.