@jospoortvliet @bert_hubert @niels @Karlitschek FOR FUCKS FUCKING SAKE.
Ok, this is a new default setting for the new sharing integration, defaulting (seemingly? now? need to dig further... -.-') to 'yes'.
and
Latter touched in a recent clean-up effort:
https://github.com/nextcloud/server/commit/669e6cadd6bcb73df3f2cf8774e8ee2e3bfb7c77
I do not _fully_ get why the behavior change occured yet, though.