The FET inputs of CMOS logic have extremely high input impedances.
They require just a little bit of charge to make the MOS channel
conducting. I have observed the voltage on a bus line (all CMOS
components)  drop sooo slowly when the output was switched to
tri-state. It took ages to discharge the parasitic capacitance of the bus
through CMOS inputs. (of course no pull-up/pulldown resistors were
used).

Your static discharge is supplying that tiny amount of charge. Solution
may lie in tying your /MCLR pin to a small capacitor, so the static
discharge goes into the cap first.

J Jing