So as not to take up space in other threads discussing the change...

From the AKC board meeting minutes of June 11-12, 2013 found at

Standing Procedure Number Eight was amended to forbid the use of layout blinds. A layout
blind is where an individual conceals himself by laying down on the ground under a
camouflaged cover.
STANDARD PROCEDURE No. 8 (third paragraph)
8. Retired Guns and throwers should be concealed by a blind that
provides complete coverage, adequate space, and natural camouflage to
conceal the distinctive shape of the blind and in no event shall gunners or
throwers be instructed to lay down on the ground in layout blinds or like
configurations for hiding purposes.

The change takes effect August 1, 2013. Information on the amateur definition is found just before the change to prohibit layout blinds.