Check and see if the "auto" light is illuminated in the center of the AC direction dial. I am pretty sure that if it is, the car will automatically determine which vents to direct air through, so even if you have the dial set to "feet only" the car may use other settings if it determines they will more efficiently heat/cool the seat occupant if this setting is on auto. In my car, when you manually turn the dial, the "auto" light in the center of the dial turns off, indicating that you have selected to manually override the automatic vent choice by designating the vents you want the air to come out of. I'll play with this later and confirm the operation.
BTW from this post and your other one about the brakes, I find your dealer's responses "questionable". It sounds like they are trying to tell you anything it takes to get you out of their hair rather than spending the time to correctly diagnose your problem and solve it for you. My dealer would never take this approach to issues like this. However, unfortunately there are dealers out there that prefer the "half assed" approach. I suggest that you call MB corporate and tell them about the issues you are exeriencing, and your dealership's responses to you. I am certain that after your dealership gets a call from MB corporate, you will find that they are MUCH more interested in spending time and effort to resolve your issues.
Good luck!!
