I frankly don’t think this is desired behavior. Especially since it breaks settings across shields and on-demand scans.
For example, I only use PUP detection for on-demand scans, but not for real-time shields. If I turn Hardened Mode ON, PUP detection gets enabled. And if I uncheck PUP detection in general settings, it also disables it for on-demand scans where I prefer to have PUP detection. It’s not exactly a cool behavior…
I do/did the same as you I only have PUPs checked for on-demand, I have just checked and PUPs are enabled, so at some point I have enabled Hardened Mode.
I was thinking it is an unfortunate consequence of Hardened Mode checking all files against the avast cloud, but that is only meant to be for, Hardened Mode, aggressive.
I have also found that having enabled Hardened Mode, on-access scan for PUPs are enabled. Yet if you disable Hardened Mode, the on-access scan for PUPs isn’t reversed.