This is happening because you don't understand how the 8 direction is working or how the mouse triggers are working.
1. Read the manual for both again.
2. A mouse trigger will happen only once per click event, which is incompatible with input controls for 8 dir.
3. Setting speed to 50 will set speed for the direction the object is facing, hence why always to the right and then slowing to a stop. Remove the speed 50 commands and change the click trigger to mouse button down and it will work properly. If you want to command a movement on a click then you need to use custom movement and set speed rather than 8 dir movement, which expects continual player input for control.
4. This should be in the "How Do I" rather than the bug section....