It looks like setting `RETAIN_OLD=YES` "solves" at least part of my issue, or maybe I misunderstand how `ucf` is supposed to work.
- Bug#925375: ucf: UCF_FORCE_CONFFNEW=1 and dpkg --force-confnew broken code
- Bug#925375: Acknowledgement (ucf: UCF_FORCE_CONFFNEW=1 and dpkg ... code
