Sandpit is right, it is a furfy. It comes back to a misunderstood explanation by SG of the new rostering system at a crew open house a few weeks back.
SG attempted to describe how 'sophisticated' the program was by using the DH crew duty as an example of how it optimises the duty times/limits. The analogy he used is that if at a cc can do a duty flight and then deadhead home, the system will do that. HOWEVER, this duty will NOT come into effect as they understand how it will effect the cc.
In anticipation of the arguments there have already been a few flights like this already - yes there were a couple of flights last month where cc dead-headed back, but they were VIP charters and they were ferried back with positioning crew.