I'm running into a screwy problem:

Using PBP and a 12F683 in a breadboard configuration, I've enabled the internal weak pull-ups on two pins, GPIO.2 and GPIO.1 (WPU=%00000110). These pins have simple NO pushbuttons to ground. I've reduced the essential parts of the circuit and program to one switch and a blinky.

The results are flaky.

Often, on power-up, the circuit behaves as if the switch is closed and held closed. Other times it starts normally, then jumps into the switch closed routine. (It doesn't behave much differently with the internal pull-ups disabled!)

This goes away and everything is hunky-dory if I put external 10K pull-ups on the switches.

ESD? Transients? A consequence of breadboarding? I'm nearing wits' end.