I see the transfer of self ownership as defective.
The master can never really own the slave's self. He can't will the slave's arm to move. He can't will the slave to love him. He can't know the slave's thoughts unless the slave shares them.
Pretend the slave sells himself to a master. If a potential master should buy another's self, he has no one to sue should this purchased self "reassert" itself. The slave could always say he had no will once he transferred same to the master.
Obviously the master has unconsciously willed the slave's body to "escape". In fact, the master has assumed perpetual responsibility for whatever future actions the zombie might take. For example, should the zombie kill the master, the master has merely committed suicide.