You can see the thread on it
here. Basically, some sort of mysterious red beam (some sort of targeting system? It seems to indicate the rough angle of the shots) hits the opponent out of the way of the shots.
It's basically how the
0% Little Mac KO move works - I position DHD to set up Mac so he bypasses the second shot (which is again, part of the 'slide glitch') on down smash A.
All of the smash moves are affected, but forward smash A is the only one who 'truly' has the glitch.
[By 'truly' I mean the red beam: only forward smash gets that. The others fail because the angle the opponent is juggled simply misses the second to third shot juggle in both down smash and up smash because Nintendo didn't properly factor in opponents who intersect DHD and thus didn't calculate the appropriate delays or angle.]