Lying on your back and placing one foot on the other is forbidden

Sahih Muslim: Book 024, Number 5238:
Jalbir b. Abdullah reported Allah's Messenger (may peace be upon him) as saying: None of you should lie on his back and place one of his feet upon the other.

1) Why did Mohammad disallow placing one foot upon the other when one lies down?
2) What moral purpose exists for how one positions themselves when relaxing?
3) Did Mohammad forbid this form of relaxation to his followers because he had an axe to grind with a certain Muslim who relaxed this way?
4) Did he do this to prevent people from relaxing in order so that those people might be agitated enough to continue in their pursuits of Jihad?
5) Why would Allah care how you position yourself when lying on your back?
6) Did Sahih Muslim include this to show the absurdities detailing minutia for some of Mohammad's rules?