I wonder if it would be worth submitting a revised drawing to the application with the dormer included to try and get the planners to admit the dormer is permitted development without actually having to pay for the LDC application.
I've asked the council if they would waive the fee due to them not uploading the right plans. I'm 100% sure that 5B was not on there previously, I think they uploaded the e-mail chain in place of 5B here:
http://documents.rochdale.gov.uk/pav/PublicAccessProvider.ashx?action=ViewDocument