I believe, though I'm not certain, that they're supposed to log you out of the online registration when you checkout. This is different from the old paper form-based registration.
No what happens is that when they register you they have to put in an end-date and they usually don't change that. When they do change it, they can in fact extend it without touching the online system by simply stamping on the physical printout that you can request for visa purposes. I used to get these printouts every year for my RP.