3 wheels on ground 4th turns
 

I have seen a few posts hinting at this question but it usually gets sidetracked.

2002 Audi A6 2.7T Quattro

With either rear wheel jacked up, but other three on ground, I can turn it freely with transmission in Park. I have seen a few references to the Quaife diff. but didn't think it was in my model.
Jacking up a single front tire and it will not turn in Park. (As I suspected.)
Thanks in advance for an explanation of this. I know I sound like a newb. But haven't seen this in any other 4WD or AWD vehicles I have owned.

Some sort of over-running clutch in the center diff?