> They are concerned about undershoot. Why /MCLR, since every pin should
> be similarly sensitive to latchup due to undershoot? Maybe that's your
> programming circuitry - connected by long wires to the in-circuit
> programmer. It still doesn't explain it completely, because the other
> pins should be similarly sensitive and require similar resistors.

The programming enable circuitry probably eventually leads to the gate of
a large P-FET that is part of the charge pump or internal Vpp switching
system. That could definitely go thyristor and drive enough current to
destroy the chip. (a shot in the dark from a man who once destroyed a
12C509JW by touching it MCLR first).

Peter

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