[opensuse-buildservice] package requirements for _service files not enforced

Since a few days obs-service-set_version requires python3. rpm -qp --requires shows '/usr/bin/python3'. But pkgs that do use that service in their _service files do not get python3 into the buildroot. Are obs-service-* pkgs forced into the buildroot without taking their dependencies into account? SLE12 and 42.3 fails because there is no python3. Olaf