Front disk brakes not releasing.

I installed a new power disk brake setup from Right Stuff on my 67 Dart. Everything seemed to fit nicely and bled easily.

On the first drive I noted significant drag on the front. I did keep the original proportioning valve in the system.

The brakes release immediately when I cracked the line at the master cylinder.

Am I correct that if the pressure is held above the the proportioning valve, it is likely a master cylinder issue?

The rear drum brakes work properly.