Water coming out of shower head without using the diverter

I installed a new faucet set in the shower, and when I turn on the water, without pulling the diverter up, water comes out of the shower head. The flow increases, when the knob is adjusted to the highest flow of the water out of the tub nozzle.

I used 1/2" CPVC from the valve body to the tub nozzle, and I am thinking there maybe too much back pressure there. I used CPVC because I do run hot water into the tub.

Will CPVC not allow enough water flow?

Will standard PVC work, without problems from the hot water, to the tub nozzle? The diverter appears to be working open and shut, as it should.