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It sounds as though the system is 'back feeding' through an earth wire.This has a tendency to cause all sorts of strange faults(like yours!).I would check all the visable earth connections as Renaults are bu##gers for bad connections of this type.
Either that or locate the heater relay or wiper relay and disconnect it and try the switches then.From there you should be able to follow where the fault lies.
I'd rather push my Alfa than drive a BMW....
Currently in Lagdti's garage:
2004 Saab 9-5 HOT Aero and a 2001 Audi A3 1.8 Turbo