Horses after being tamed don't show open button after in order for the player to add saddle and armor.
Steps to reproduce
- Spawn an adult horse using spawn egg.
- A button that says "Mount" will show upon riding the horse.
- After the horse is tamed no "Open" button is shown in order to add saddle and armor to the horse.
You should see an "Open" button after the horse has been tamed while you're on the horse.