Mine does this too. My understanding is that the system can air up, but doesn't vent to drop the rear end. What happens is that when you jack the wheels up, air is getting sucked into the air portion of the rear strut, as the spring is extending the strut to the extreme. When you put the car back down, there is enough air in there to keep the car higher than it should be . My car, being that the struts are likely the originals leaks down within a minute or so. Let it set overnight, and see if it comes down any.