H. G. Muller wrote on Fri, Apr 17, 2015 08:42 PM UTC:
I suppose moving your King destroys your rights to castle, as usual. The King can apparently end on the square occupied by the Rook, but not beyond it. Note that in Chess960 the Rook is also not considered an obstacle for the King move. I guess the designer did not like the King moving to the edge because that would make the Rook stationary. He also does not allow castlings where the King would remain stationary. (In Chess960 both of these can occur.)