it's kind a little complicated then. Mine doesn't do that

normally a dealer should provide couple months warranty at minimum. if not, what is the point buying from them not from private? if this problem persists, find an euro car shop specializing in auto electric, as this kind of things involve with electronic which is not every-shop-can-do...

go to this user group maybe other people can help you:
http://www.benzworld.org/forums/w210-e-class/