I never tried it, or if it did I never noticed, it just stuck right around fifty and would stay that way for a bit. I would come back to it a day or two later and it had dropped.
That's interesting, I'm wondering if when you back up it releases the pressure on the cable and it drops to 0. IF that's what it is.
It's just too weird that we have/had the exact issue, after doing exactly the same thing to our cars.