They don't always get it right....see the above posts and, as said before, reference 12.D.4.a of the PWA which expressly states:

"A duty period that contains an FDP and ends in a deadhead flight segment will be scheduled to be at least 30 minutes less than the pilot’s applicable FDP limit under Section 12 D. 1. – 3. from report to block-in of the last deadhead flight segment. A pilot will not be rerouted or required to depart from the gate on a deadhead flight segment that is scheduled to block in more than one hour beyond such limit."