"Derrick Early" wrote in
:

A little while ago I asked if the VSI, altimeter and airspeed
instruments should jump when closing the door. The answer is that
they should not. We had our static system tested and the mechanic
found a leak. As a result, we were getting cabin pressure for
altitude our altitude readings. I think that I'll add this to the
check list.

You were probably getting something between the two - meaning you were
probably flying a little high.

In Piper aircraft there is that little pilot vent window. Makes a good
leak test - at altitude open it and then let it pop shut. If the needles
jump, you've got a leak.