Because the X3d window is embeded in GM window,when you click your mouse,you clicked the X3d window,not GM's so GM can't get the input.
1) Anyone know why i cant use mouse button events? I want to use MouseLook() when the right mouse button is pressed only for certain 3rd person reasons...
You can use keyboard_check_direct(mb_left) instead.
It happened again,Xception released a great engine but without a documentation and disappeared.