Retail sales pumps are not supposed to have a lag, and are supposed to be metered from above ground. There could be a software glitch/hack/scam there, but there is definitely a wetware glitch in letting it stay in operation.
My most likely suspect cause is a leak in the dispenser, after the pump gauge. Possibly inside the hose itself. If there is a vapor recovery system in place it is probably recovering the leak from the inner layer of the hose to the outer, as designed, but if so there should be an alarm going off somewhere in the building.
