I found this link to a discussion about the Mamiya leaf shutter lens that may be helpful:

Leaf shutter question

I am not sure what model camera you have. It looks like the power winder option has the ability to control the cocking of the leaf shutter. This may pertain only to newer models of the lens/camera. Otherwise, you have to manually cock the shutter each time. I have to do the same on my Rollei SL66 with leaf shutter.