Low Air Flow from Front Vents When Rear Climate is on

[ltemup4650]

Hello all. 2011 E70 LCI here. I've read several threads on climate issues trying to find a solution to my issue but can't find exactly what's going on with my X5.

Here is what my issue is:

When I have the main (front) fan on full blast, I'm happy with the amount of air flow in the front vents. When I switch on the rear climate, the front vent air flow reduces significantly. It is about a 25% reduction when the rear fan is at its lowest setting and a whopping 75% reduction when I have the rear fan on full blast.

I don't understand why the front vents reduce so much. It doesn't seem right. Anyone else having the rear air robbing the front vents that much?