I should have mentioned that I had pre-selected seats for all 4 sectors. Only Doha to Singapore threw up this message, all other seats were as I had selected, so something was going on!
Just checked back today and sure enough, my seat is back, but the plane is now a 787. It could have been worse!
Would they have switched from a 777 with Q-suites to a 787 just because there was a light load?