I meant to say the %service_del_postun macro defined in /usr/lib/rpm/macros. The reason why DISABLE_RESTART_ON_UPDATE=yes has no effect at all is that this variable is set by a script /etc/sysconfig/services which is sourced before the variable is evaluated. Since the intended use of this variable is tantamount to not to execute %restart_on_update and thus %service_del_postun at all, let's remove this line entirely.