Your P99 is working just like it's supposed to. (Unless you have a P99QA) If you had a pistol with a hammer, lets say a Sig 229 and you pull the trigger. The trigger mechanism cocks the hammer back and then lets it fall, hitting the firing pin, which in turn hits the primer, causing the bullet to be fired. Then the slide comes back and cocks the hammer automatically. Thus now we are in single action mode. If you push down on the decock lever you put the gun back into double action mode.
The same thing happens in the P99, however the P99 is all striker fired. (no hammer) So when you see the cocked indicator pin, you are actually looking at the end of the striker, which tells you that the gun is in single action mode. When you hit the decock button you are simply putting the gun back into double action mode.'
Now on the P99QA the decocker would render the trigger inoperatable unless the striker was cocked via pulling the slide back, because it is a single action type of gun.
The same thing happens in the P99, however the P99 is all striker fired. (no hammer) So when you see the cocked indicator pin, you are actually looking at the end of the striker, which tells you that the gun is in single action mode. When you hit the decock button you are simply putting the gun back into double action mode.'
Now on the P99QA the decocker would render the trigger inoperatable unless the striker was cocked via pulling the slide back, because it is a single action type of gun.