OK, i've only had the car a few weeks so I don't know if it does this under other circumstances. With AC set low - 65 degrees - fan up full - auto off - recirc on or off - the center vents seem to shut down in traffic and air is diverted up to the defrosters - dial is open and it seems to be doing it purposely.
With the auto feature off you have a choice of blowing downward or upward. You should see a little symbol with arrows showing air flow. I run with auto on and the center vents blow.
Linear Mode
