On my sisters 2004 Z4 3.0i the climate control always has the vent for the winshield defrost on. Even when the knob is at full floor (she has the manual climate control) it will still blend to the defrost for the winshield and the door.
This has become a safety concern

as the winshield will inevitably fog
up from the outside due to the defrost vent always being on, this requires the car to have the windshield wipers on int. even during the daytime.
Thanks for letting me vent.

Any suggestions on a fix, anybody have a similar problem on a 2003 and later Z4?

I have a feeling it is simply a "blend door" in the HVAC system that is not opening and closing the defrost vent completely. The techs think it is "normal"

what a joke.