Welding Regulator Leakage

I hooked up an oxygen regulator to a tank and opening the tank valve
slowly it registered about 2200 psi. To check for the seal at the
regulator connection I then turned off the tank valve with the regulator
closed so that the gage was reading only the pressure of the few cc's of
gas trapped between the regulator and the closed tank valve. The
pressure would drop about 25-50 psi per minute. It should be zero no?

John