horse gets hurt when i dismount it and other bugs

when i dismount a horse it gets hurt on one occasion a horse was killed even tho its health was full it only happens when you press shift. i also have two other bugs when using a bow when i go too shoot it its like am right clicking really fast but am not the same thing happens when i try to eat food its like the computer is telling the game you cant do that it could be a fault with my mouse but as far as am aware there are no faults. after further investigation i have concluded that there is a fault with my mouse when i play this game my mouse is fine its just when i play there is a fault.