Thank you for your replies, as ckx2 said it was because the aircraft has Q suites. I now remember from somewhere in the Qsuite thread there was a mention of seating policy and I think it went something like this for solo travellers:

1. If window seats are available then solo travellers get assigned these.
2. If all window seats are assigned then the "group" seats are blocked until closer to checkin so that QR can allocate group travellers as required with the remaining solo travellers being "tucked in" to fill up the space.

When I booked almost all of the window seats were taken, what caught me out was the 4 window seats (1A, 2B and 11B and 11J) that were blocked. I called to ask for a seat and curiously the agent could not allocate any of the blocked window seats and allocated me 2D instead saying that the blocked seats were under airport control. He did say that he would put a request into the airport to move me to 1A if possible.

Anyway, It was not a cause for concern, it was simply part of the QR seat allocation policy to get families/groups together where possible.