There was a simliar suggestion, Hipennine, on Flyertalk sometime ago, with regular pax of the Singapore and Narita routes saying they are the absolute worst BA experiences to be had anywhere. Being in the know about who reportedly gets first dibs on those routes, they were surmising a similar reason. But who knows.
A few said that after some appalling trips, they kept BA for all of their other regular travel to keep their Gold and Silver status, but went to other carriers for those two routes.
p.s. BG, you present a thorny imponderable. What if those Unite or BASSA members who have transferred to mixed fleet received a ballot and voted by mistake? Oh dear! That should give BA's lawyers something to do on Monday.