There are two bugs with horses.
One: if you are ridding a horse and try to pass over a 2x2 door (like a wall of blocks without a 2x2 secction) you will suffocated in a wall.
Two: if you do the one bug with the 2º third camera, when you pass the door or the wall the camera changes to first person.
One bug per report, please. It's hard to track what has been fixed and what hasn't when there are multiple bugs listed in one issue. Your first one is a duplicate of MC-13668, so you should edit it out, and change the title to focus on the second one, which hasn't already been reported.