Some time ago (I think January?) it was discovered that even though we set force=1 on the recovery checkpoint, this does not prevent it from skipping some trees and not checkpointing them. In particular, even with force the checkpoint only includes trees that are open; trees that are not open are skipped. This happens separately from the overt skip logic, so it isn't entirely obvious, and came as a bit of a surprise. And since we had been in some cases reasoning about things based on the assumption that the recovery checkpoint isn't skipped, it was a bit of an unpleasant surprise.

Consequently it was decided that if it's going to be skipping trees anyway, we might as well turn off force on the recovery checkpoint, and furthermore if anything breaks as a result we want to know about it.

Actually posting the change got postponed for various reasons and then temporarily forgotten, but now that releases have been branched it now seems like a reasonably good time.