If you get on the boat to go to DTD at POFQ and it is on it's way to POR then you have to get off the boat at POR and reboard, it will then stop again at POFQ to go to DTD, at least that is what the sign says, have not experienced this actually happening since we got on at POFQ on the return trip, late afternoon, not busy at all.
Be warned that when returning from the parks the wait for the bus was usually quite long, on the evening of EMH at Epcot we waited through 6 PO busses before we got on, we left the park at 10:30, I am sure the wait when the park closed was huge!! Everyone was pretty good natured about the whole thing and that makes a big difference when your waiting...
Bev