New @a[dx,dy,dz] not working correctly

Using the command '/testfor @a[X,Y,Z,dx=0,dy=z,dz=0]' will still test a player that is on another block. In the picture, i am standing on a lamp, The on my curser is set on is the one i am testing for. It is still testing posative for me on a different block even though the direction is set to 0 and should only test if i am on that block, not the one i am standing on.