Pretty much the best explanation of it here. Also the window for special move motions is just ridiculously long.
Il use Green Lantern as an example of what I mean. Suppose an opponent is on top of you pressuring you and your crouch blocking and your opponent ends in something negative on block. So you as the Lantern player attempt to go on offense with your B13 string. Because you were holding down crouch blocking if you move directly to Back for B1 the game will instead read it as Down, back 1 and give you Lanterns Might(a very unsafe move if blocked up close)
The reason for this is because in moving from down to back you are passing through the diagonal direction Down/back and as SAO said the MK controls only recognize Up down left right, but the game reads the diagonals as well. In essence the confusion between the way the controls work and the way the game reads them lets you hit the same direction(in this case down) twice. You are already holding down crouch blocking(That's the first down, which is not read) and then when you move directly to Back(moving through Down/Back, this is what inadvertently make it come out as a special move)
Basically the only guaranteed way to make sure you don't get random special moves in normal controls is to:
1. Make sure youre left, right, down, up executions are dead on accurate. (Difficult on a square gate stick because there are no corners for up,down,left,right)
and
2. Whenever you are already holding a direction( such as crouch blocking or walking forward or backward) you must make sure to release the stick into neutral before doing any normal moves that require a directional input as well. Neutral is like hitting reset in the games reading of your commands so that any previous directions you were holding are not combined with the directional of the move you want.
There is a window where you can pass through neutral and still get special moves(such as Back,Foward or Down, up moves) but this is a faster window and is intentionally there as opposed to the enormous window your getting because of the way the game reads directionals.
TLDR:
all in all the controls are fucked, somebody get me an advil.
