Important rule of US DM redemptions: The reason the agent tells you when they reject your itinerary is not always the correct reason.
Of course you can connect through DOH twice. There's not really much restrictions around going through the same city twice.
That itinerary has been booked before by an AFF member so unless they got lucky I'm not sure where the system is breaking down.
Thanks for the confirmation of my understanding, however I have called twice and moved from the Agent to a Supervisor on both occasions and the response has been from everyone that the routing is being rejected by the system as invalid. They are indicating that its not their decision. The booking is on hold so I can try to find some other way to do one of the legs. It maybe possible via LHR and HKG and come in under MPM, but of course it will be at a cost because BA will be involved.
It seems to be pointless to phone again, the first call was over 2 hours and the second was 50 minutes. Maybe if I let the on hold lapse and start again it is worth one final go.
I wonder if some of AA rules are creeping in as I informed them that I have other bookings where I am transiting through one city twice and this was not a problem. I was informed the problem was specific to DOH (ie Middle east).