[opensuse-buildservice] change of docker image filenames

In the past days, or perhaps weeks, the name of docker images changed. It used to be 'foo.tar' in the 'osc ls -lbv' output, now it is 'foo.x86_64.<release>.tar' How can I restore old behavior which provided predictable filenames? I think it was controlled via '#!BuildTag:' in the Dockerfile. Olaf