I booked a flight from MAD-LHR on the A340-600. It is operated by a three class frame with PE. I was unable to book seats at all when I made my booking and got assigned a random window seat. (This was due to my BA Frequent Flyer number attached to the booking, booked on iberia.com)

If I do a dummy booking, Rows 11-15 are available in a 2-3-2 configuration but when I rang them they said they were "restricted". Why can't I select them despite being able to book if I bought a new ticket?
Any ideas?

Thanks