further testing points to https://github.com/openSUSE/obs-build/commit/49eb995467bcbb03b74cd15adf919691c8ab582b#diff-8052220fc3d167573cede2c5b650b8ffR514 which for me expands to if test 0 = 0 -a -n /var/tmp/build-root.4 -a /var/tmp/build-root.4 = / ; then so that if would evaluate to false where it was true before.