Hi, Paul,
I think we are talking apples and oranges. On the PP/PPK, when the hammer is dropped with the safety, the safety catch itself rotates up around the back end of the firing pin and its internal surface also blocks the pin by blocking the shoulder on the firing pin itself. If a PP/PPK fires when the safety is engaged, either the safety or the firing pin is defective. (And the pistol will fire full automatic until the magazine is empty.)
This has nothing to do with the hammer block, since the hammer and trigger are back when the safety is engaged to drop the hammer, and the trigger will remain back until the safety is moved to the fire position.
The hammer block, as I said, is in the frame, not the slide, and is disengaged when the trigger is to the rear, just like the block on a revolver. Whether the safety is engaged or not, the hammer block prevents the hammer from moving forward. When the gun is carried with the safety off, the hammer block prevents firing if the gun is dropped on the hammer. Since it is spring loaded, it is not quite as fool proof as the mechanical hammer blocks on a Colt or S&W, but it is very reliable.
Jim