>Would you kindly point me to a page and line where it says that a negative
>voltage WRT Vss on a pin violates the operating conditions?

I do not have the data sheet for the 16C622 which I believe you are using, but I
looked up the sheet for the 16C6x (DS30234D) and page 183 lists "Maximum ratings
any pin to Vss as -0.3V to Vdd+0.3V, i.e less than a diode voltage drop outside
the supply rails. This is listed the same through subsequent pages for the
various models of this PIC.

Page 186 gives "Standard Operating Conditions" i.e. the conditions it would
expect to operate under as Parameter D030 - Input Low Voltage Min Vss - not
(Vss-0.3V)
The next parameter is "Input High Voltage" Max Vdd - not Vdd+0.3V. the following
pages list the same for the other models of this family.

I also checked the data sheet I have for 16F87x (DS30292A) and this gives the
same set of voltages for the same parameters. I repeat that "Maximum ratings"
are the limits that will not destroy the device, but are not "standard operating
conditions". All micros, digital and analogue ICs, transistors diodes and
practically any component I can think of is specified this way.

An application note which shows a resistor being used off the mains to drive a
pin does not necessarily give licence to use a chip like that. A collegue I
worked with always said "It is not what is in the circuit on the application
note, but what they left out that is important", and he is right. The device
used in the app note may have happened to work because an adjacent pin wasn't
used, or the chip was a preproduction one that had a different mask pattern, and
the circuit designer was lucky and got away with it. It may even be that the
circuit he used had the same problem you do, but the circuit that got printed
did not show the mods used to get around the problem.