Thanks Shock, I had already done everything you mentioned trying, minus reseating the 89c51 and actually taking measurements beyond resistance after reinstalling the original switch. I noticed an odd bit of reddish discoloration on one of the pins very close to the packaging. Definitely not messing with it until I hear from Pace, but might get a closer look under the microscope. To be clear, the button does allow me to move through the setup process. I can save my settings fine and proceed soldering. Everything is reset after I power it off. Password, timers, and temps are all wiped. It starts up as if the program button had been held down while power is switched back on and enters setup automatically.
Edit: one further thing to note is that I also powered it on with the switch completely removed and it still entered setup