[wadeintothem]

The rule prevents a player from standing 10 yards into the outfield and timing his running start so he tags his base right as the ball is caught/touched - thus he cannot be appealed out, but he is already at a full speed run on the way home at the moment of the catch/touch.

And yes, I would expect an umpire to see that a runner was lining up behind the base as we are expected to see anything else...