That does sound like a bug, the planner should be inlining all of that. I would mention it on the postgres mailing list so a committer with more experience in how the planner marshals all that stuff together can weigh in.
I guess I got nerd-sniped. I dug a bit deeper into what was happening and the issue is the new version of the function called to_char() which turns out isn't IMMUTABLE which broke the inlining!
