I never posted the resolution to this... it ended up being the master cylinder that had gone bad. Replaced that puppy and the brakes stopped dragging/locking.

 

I should have thought of that.
There is a return check in the master.
It's there so you can bleed or pump the brakes.
It has a small bleed back hole in it to let off the brake pressure.
If that bleed hole gets clogged, guess what?

What clogs the hole? A worn out master.