Hi, when basic-suite-master OST is run with cluster level < 4.2,
verify_backup_snapshot_removed test fails.  Indeed, the snapshot removal
fails, with error such as:

  [c784a2c3-a700-41f7-80bd-2d1e25a712c5] Failed to live merge. Top volume 15b82854-c9dd-44aa-83c9-aebe273ac6a4 is still in qemu chain [15b82854-c9dd-44aa-83c9-aebe273ac6a4, 3c21269c-e71b-4e96-977e-a9168bbba9bf]

See
e.g. https://jenkins.ovirt.org/job/ovirt-system-tests_compat-3.6-suite-master/52/artifact/exported-artifacts/test_logs/compat-3.6-suite-master/post-004_basic_sanity.py/lago-compat-3-6-suite-master-engine/_var_log/ovirt-engine/engine.log

Does anybody have an idea what might be wrong?