Standard Bugzilla source requires two separate changes to be performed to set a status of a bug and also change the owner. Red Hat Bugzilla allows changing one or both of the attributes in a single action.
This is already implemented in a better way in upstream trunk. We will just
convert to doing it the new way and get rid of the current.
In upstream, assigned_to is an editable field with a checkbox below that you can
check to set to default.