GTK derived palette regression in 6.6.1

Having updated to 6.6.1 from 6.6.0 I'm seeing some unexpected changes in the colours that are (presumably) derived from the current GTK theme. On Ubuntu 20.04 with the "Yaru" theme I get the following under 6.6.0:

But on 6.6.1 I get:

Some of these selections are actually improvements in 6.6.1 – inactive highlight being blue under 6.6.0 seems odd for example – but others just look flat out wrong. In particular it doesn't seem right that in every state, light, mid and midlight are all the same colour. I've tried a whole bunch of different themes for what it's worth, and they all exhibit similar regressions.