Heated mirror goes on when window goes up!

[PCrighton]

I have a peculiar problem:

When the window (driver's side, RHD), reaches the top limit, the heated mirrors often come on!

If the window is down and I press the up button the window goes up. Quite often as it reaches the top the light on the heated mirror's illuminates.

If the window is already up then as soon as I press the up button the heated mirror light often illuminates

It doesn't happen as it goes down nor on the passenger window.

Anyone had the issue and resolved it? It didn't happen when I bought the car but has for quite a while now and I think it's more regular.

[Steve Tinker]

Two things come to mind: 1) moisture @ the mirror wiring connector behind the door card and 2) faulty electrical portion of the ignition switch.
My heated mirror indicator light used to come on after I washed the car - found moisture caused by a leaking plastic membrane behind the door card.