Certain key combinations not working

I use 2 behaviors taken from the Garagegames website AsteroidControls.cs and shoots.cs

In AsteroidControls.cs, I use the following code:

%template.addBehaviorField(upKey, "Key to bind to acceleration", keybind, "keyboard up");
   %template.addBehaviorField(leftKey, "Key to bind to rotate left", keybind, "keyboard left");

In shoots.cs, I use the following code:

%template.addBehaviorField(fireKey, "The key to fire the projectile with", keybind, "keyboard space");

However, if I hold down Up, then Left, then Fire, the first two keys will register making my avatar go around in a circular motion, but he will not fire.
If I hold it down in a different order, only the first 2 keys register and the third key is ignored. This problem arises with LEFT, UP, and SPACE used in combination specifically i.e. if I hold down LEFT, DOWN (instead of UP), and SPACE all three keys register and I go around in a circle firing stuff.

This problem also arises for certain combinations of keys like UP, LEFT, G and DOWN, RIGHT, NUMPAD0.

Does anyone know how to fix this and allow all three keys to be register when held down simultaneously?