Digdoug used up all his juice before he fled the city in order to rig up the Tower as he had planned, just didn't get the chance to really properly finish the job. His orders didn't tell him what to do with his Juice that day, so he filled in the gap with his Duty. The orders did say to leave immediately, but given the relative nature of time in Erfworld and the fact that he was on-turn, the term "immediately" is open to some interpretation. So much like his king seems to be fond of, he obeyed the letter of the orders but not the spirit :p
"I'm afraid I don't understand. And also afraid that I do."
Two guys with basically the same name in a discussion about a character getting cloned.
There's gotta be a good joke in here somewhere.