I've never heard of that rule.
This part of the rulebook seems to cover what happened on Morgan's steal.
5.09 The ball becomes dead and runners advance one base, or return to their bases, without liability to be put out, when—
(e) A foul ball is not caught;
I don't know how you guys feel about Oswalt being thrown out but I didn't like it. I know it benefits the Nats but that's not the point. People have complained about the Nats being shafted by umpires in the past because they have been bad and it may be happening to the Astros right now. I think the umpire could've given him a little more rope to hang himself before ejecting him.