Huben K1 - slow pressure restoration by regulator

I have a Huben K1( version 2 ) equipped with an externally adjustable regulator. After firing a shot, the reading of the pressure gauge ( at the regulator output side ) will instantaneously drop by about 10 bars and it will take about 10 seconds for it to restore the preset value. may I know if this is normal ? if not, what could be the cause ? 
 
this is not a normal situation, we have come across this two times, there are several outputs .... 1) if you have a dealer to replace the regulator 2) to go through the regulator completely with the replacement of rubber rings, saddles and polishing. 3) put the huma. We decided the way 2))

Forgive my ignorance, may I know which part is the saddle and where should polishing be done ?