Tried mine today after reading through this post earlier. Sitting at school waiting to pick-up the kids ACC set to a comfortable 70dF or so on "auto", fan running at low speed.
I hit the defrost switch, air moved to the windshield and turned HOT. Soon as I switched back to bilevel, the air was coming out as cool as before.
That makes three, sounds like normal.
I'd guess that for normal inside window fog, bilevel would be fine, but for the first warm of the windshield in the morning, or dead of winter driving, then use the defrost button.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.