[Symon]

You're not even checking if the player is riding the horse. So according to your code i can press SHIFT, ALT or SPACE to move even without riding.

Also i don't understand why you declared "angle" twice.

Imho, this should be a snippet, not a filterscript. I don't see anything that's valuable to be "copied and exhibited everywhere".

To everyone asking a video, imagine a horse having convulsions to get the idea. (This is what happens when you press multiple keys at once)