What on earth is going on with rebinding keys on this game?

Bind Mouse 1 to something on helicopter flying =

OKAY I GUESS YOU WANT TO UNBIND YOUR SHOOT BUTTON ON INFANTRY THEN?

Bind something to spacebar on helicopter flying =

HELLO SPACEBAR ALSO FIRES YOUR MINIGUN, OH NO ITS NOT IN THE BINDINGS AT ALL IT JUST DOES THAT

What the hell is this? Its impossible to rebind your flying keys when flying keys remove your infantry keybinds....?