I've started to notice that when I attempt to go from grounded to jump > up air quickly, my character performs an up smash instead. I started experimenting to try to narrow down the source of the problem and I think it has something to do with input buffering. When I'm holding up on the control stick and I'm just finishing an attack (such as up tilt), pressing X immediately followed by A frequently results in an up smash, instead of my character jumping and performing an up air like I expect.
Now, I would understand my character not jumping if my jump press was too early for the buffer, but then I would expect another up tilt because I have already been holding the control stick up for some time (I didn't just "smash" it up as is required for a "smash" attack) and if I wasn't buffering this combination (standing still, holding up, push A) the result would obviously be an up tilt.
Why does my buffered input result in an up smash?
Edit: Not that it should matter, but I did this testing on the 3DS version of the game.