Yep this has been posted several times. You just stated, and my point is, that nowhere does it ever say over a moving vehicle. You can see this ASSUMED all over the web and in different articles, but never an official regulation. We have looked for years and noone has ever been able to provide it. If you have it please share.
I have no reason to do this and would never condone it, it is just an example of the horrible vagueness of specific common and very dangerous situations that the regulators need to clean up. It is way to hard for people to understand clearly. Otherwise there wouldn't be a thread like this... and there shouldn't be.