How do you miss that call? That's what the homeplate umpire is supposed to be looking for.
I've said it before: Alan Porter is a HORRIBLE umpire. He's made some bad calls before, but this takes the cake.
http://washington.nationals.mlb.com/video/play.jsp?content_id=24900029&topic_id=8877508&c_id=was - the last couple seconds of the clip clearly shows that the runner was nowhere near the plate. Porter never even looked at the runner and just made a guess when Mattingly came out.