I'll try it without pictures first if you don't mind?
Look at the bit of the propeller which is on top of the propeller disc. It's going to the right, assuming RH spinning propeller.
Now, pitch down. You have to make the bit going to the right go to the right and forward to make the propeller dish pitch down. This means exerting some torque on the propeller disc.
Then, the same bit of the propeller comes through 90 degrees of rotation and is now to the right. Here, it has to go straight down again and not forward or aft.
A further 90 degrees of rotation and said propeller bit is pointing straight down, going to the left... and due to the pitching also moving aft.
In those 180 degrees of rotation, the bit of propeller has gone from moving forward to moving aft, on top of the rotational movement of the prop. This means it has to have been accelerated to the rear. Equal and opposite reaction dictates that it must have exerted a force on the rest of the aircraft to the front during the half-circle on the RH side of the disc.
The torque you used to accelerate the bit of propeller forward comes back 90 degrees of rotation later as a result of all the bits of the propeller having to go from going forward to going aft.