Heated mirrors only work when the heated rear window's switched on, they stay on for 10 minutes then turn off.
My Cupra has them, but its an MY05.
Well I'm glad to see that VAG has moved forward to emulate the way VX did things back in 1991!
My 2000MY Passat ended up with me burning out my mirror heaters when I thought that they were controlled by the rear window heater - I should have read the owners handbook properly, instead of finding out about this (too late) in the internet!
I jumped into my wife's 2003MY Polo tonight, and yes she has forgotten and left the mirrors on for the past five days - time will tell if they survived this!
Actually my 2000MY Passat does not even have a rear window heater timer - just a switch!!