FTR, it's not just about having a /run/systemd/generator/tmp.mount if you have an fstab entry like "none /tmp/ tmpfs defaults 0 0", because with that "systemctl --quiet is-enabled tmp.mount" fails and thus shouldn't be added to was-enabled. So I still cannot reproduce this nor have an idea what's going wrong here.
FTR, it's not just about having a /run/systemd/ generator/ tmp.mount if you have an fstab entry like "none /tmp/ tmpfs defaults 0 0", because with that "systemctl --quiet is-enabled tmp.mount" fails and thus shouldn't be added to was-enabled. So I still cannot reproduce this nor have an idea what's going wrong here.