The water heater is on, and full of hot water. The coach is hooked to city water. Shower is going fine, temp is adjusted just right. Part way into the shower I turn the water off at the shower head. When the water is turned back on at the shower head, there is a rush of hot water for a couple of seconds, then the water returns to the adjusted temp. Why the hot water?
One possibilty, and I need more information, is that when you use the shower head shut off you confuse the water mixing valve and there is greater pressure on the hot side (for whatever reason) and when you release the flow the hot side gets through first.
Is the control a single valve or do you have a hot knob and a cold knob? If it's a single than that could be it.
The only thing I can think of is that the water in the heater gets under more pressure due to being heated. I don't know if there is a one way valve at the inlet to the water heater, but perhaps that would account for the higher pressure, thus the short rush of hot water.
I just thought it very strange. It's OK as long as you know it's going to happen. Sure was a surprise the first time.