When you obtain items with an invalid tiledata using external editors [for example an arrow with the tiledata 99], your minecraft and the minecraft of the host of the world you're currently in crashes (the host only crashes if the item gets dropped / put into a player's inventory), (and every player gets kicked). This occurs when:

• getting the item into your inventory
• breaking a container which contains one
• opening a container which contains one
• selecting the item with your mainhand
• trying to clear it using commands