>Not necessarily so.  The structures that sustain the flyback current are
>not necessarily the same as those that conduct the forward current, and,
>if sufficient current flows into the substrate, the whole chip can turn
>in to a thyristor!


I beg to differ. Please check the data sheets, and you will see something
like this:

"Input clamp current, IOK(VI<0 or VI>VDD).....+-20mA"

I realize that output current is rated at 25mA, but the fact of the matter
is that PICs have good protection on most of the pins, they are not your
average CMOS chip.

Cheers, Bob