Mirror Shield glitch

Intro
The Green Shell Glitch is what happens when two Pits use their Mirror Shield to deflect a Green Shell 5 times.

What Should Happen
Normally, after a green shell is deflected 5 times, it would cause a Shield Break. Instead, something else happens....

What Happens
Instead of a shield break, Pit is pushed backwards taking no damage.

Why it Happens
It is currently unknown why it happens