Well yeah:

  // then scramble
	var r1, r2;
	for( i = 0; i < numpieces>>1; i++ )
	{
		exchange( Math.random() * numpieces >> 0, Math.random() * numpieces >> 0 );
	}

Easily enough fixed by just "manually" sliding a random piece adjacent to the hole a couple thousand or so times, but yeah... Making any sort of game, no matter how simple, is harder than you think :\