No you don't miss anything. The big problem of OpenStack is this - when some bug/issue happen the DB stuff (not only) is in inconsistent state, unfortunately OpenStack don't try to fix the inconsistent state.
So you created the volume, but in process of creating task you reach the bug. So volume was not created and the database include record about creating.... :(. Now you have to know the procedure which openstack does and "revert it manually" (update DB records, handle iSCSI tasks,....)
No you don't miss anything. The big problem of OpenStack is this - when some bug/issue happen the DB stuff (not only) is in inconsistent state, unfortunately OpenStack don't try to fix the inconsistent state.
So you created the volume, but in process of creating task you reach the bug. So volume was not created and the database include record about creating.... :(. Now you have to know the procedure which openstack does and "revert it manually" (update DB records, handle iSCSI tasks,....)