... is there a connector in the loom they might not have clipped in properly?
in the A-pillar passenger side
Rear electric windows will not wind up until they have wound down fully, from any open position. If you try to close them, they go up about 2cm and then down approx 5cm and stop, this repeats until they reach the bottom, then they will close fully. This happens with both the switches in the drivers door and on the B pillars.
happens to my 06-2005 C8 too after a while of not having opened/closed the rear windows - completely open/close them a couple of times after each other and the pbl is gone
The fan blower for the rear appears to have packed up, I get the indicator show on the LCD but no increase in air flow - can it be accessed to check it?
put them on max. on the B-pillars while LCD indicator shows the rear blower (then they are activated separately) - should work although don't expect a storm 
I've had many niggling problems with this car which is such a shame because I really like it when its working! - - rear tailgate fouling on the light clusters
specific pbl on earlier models (my 2003 C8), resolved on my 2005 C8 (a little smaller light clusters), non retracting seatbelts
sometimes the belts on the 3rd row are indeed, but pull them out and in a couple of times and....... , seat rail covers breaking up
again specific on earlier models, a new cover wouldn't cost a fortune, I think, air leaks from vents in drivers door to rear passengers
again specific on earlier models, I think there are other rubbers available for the front doors which resolve this, interior lights staying on
never had that on my 2003 C5, water leaks from front door seals
a little when going trough the car-wash high pressure cleaner, excessive front tyre wear (even on 16" rims)
put your front tyres at 2.6bar, take roundabouts very quietly and it'll be much better - my experience and brake wear
this is strange - I replaced front pads only @ 97.000km and the rears are still OK now @ 139.000km, but I don't have ESP on my 2.0HDi of 2005, which can explain a lot specially when you are a 'sportive' driver: ESP will react frequently and use your brakes - a C8 is a heavy car, electric sliding doors refusing to close
don't have e-doors so can't advise, washer pump failure (3 times)
specific on earlier models again, poor fuel economy (28mpg) and performance
2.0HDi is more economic but worse in performance - not using the airco too much will help keep consumption down, my experience- now improved with tuning box, poor radio reception (even Radio 1 is difficult to get sometimes), front seat base foam disintegrating
stays a weak point of the EV2, rear seats jamming & refusing to fold or move, aluminium coating on handles peeling off plus more
specific on earlier models, later on they were painted grey and no pbl anymore - my dealer replaced them under warranty for painted handles on my 2003 C8. I've had some fixed by the dealer but many issues remain, now the cars out of warranty they wont entertain fixing anything unless I pay - even the stuff that has been reported but not fixed while the car was in warranty - they say the car's done "extreme mileage" even though its supposed to be covered by a 3year 60k warranty...!! To be honest, what they did 'fix' has been shoddy work and I'd prefer to sort things out myself if possible, or go to an independant...
Appologies for the long post, any help/advice will be much appreciated!