I honestly think this is part of BAs insidious plan to "encourage" all passengers to pay to pre-seat, or to fly enough to attain status and therefore pre-seat for free.

I fell victim to this in August flying CE, when as a family of 4 on one PNR we were scattered liberally throughout the CE cabin.

It happened to my mother last weekend, when she flew with my sister GLA-LHR on a half-empty flight ---- when they got to check-in, my mother had been seated in 4A, and my sister had been put in row 16 ! Again, 2 passengers on one PNR, arbitrarily seated wherever was least convenient !