Yeah, so basically, every single time your press a button, the game reads it twice. When you press it, and when you release it.
The window in MK9 is so big it's ridiculous. You can
release then do
,
,
and the
special will come out because the 2nd input is still on the buffer and will take priority over
.
That's why it's so annoying to a lot of players. You can avoid negative edge by simply not releasing the button you don't want the game to read twice. This is especially useful if you have a stick because on pad it's kinda hard to do.