This isn't a glitch, its programming a new hitbox. I would like to recommend changing the players hit box when flying with the Elytra. I was playing with them today, because they are lots of fun to use. I was trying to swoop in with them on a hoard of zombie-pigmen, trying to hit them, but I found I couldn't do it without landing on the ground. So I tried it in 3rd person, because it looks better like that, and because its easier to fly. But I saw something peculiar. I was flying right through them, but I couldn't figure out why I couldn't hit them. So, to solve it, I turned hit boxes on. The player's hit box was shaped the same way they are shaped without flying with the elytra. The real eyes of the player are far above what they look like from the outside. This doesn't look right, as you can see in the supplied picture below, and it also messes with the functionality of the Elytra, as you hit will your "head" on a block above you, even though it doesn't look like that from the outside. I would ask that you programmers to change the hit box while in glide mode. This way, you can still be able to swoop into mobs or players, hit them, and still be able to fly away unharmed. I would recommend making it 2 long, 1 wide, and 1 high, with the hitbox always following directly behind the "eyes" of the player, so that it always looks right to the flying player. This proposed orientation is if you are unable to change it to be angled diagonally. (And center the player to be in the very middle of the screen in 3rd person, its hard to see the ground normally.) Also, for one recommendation, to give an original chestplate looking thing to the Elytra, that gives it about as much protection as a leather chestplate. In total, a full diamond suit - the diamond chestplate + the Elytra would make a player as strong as full Iron armor, with the ability to glide, but limited by the hight they could get to. The main reason why Im recommending this though, is because pants without a chestplate look horrid. Also, because I love the Elytra, and because I want them to be as perfect as possible, I would ask that you get rid of the barrier that keeps you from looking straight up, and then looking backwards. I understand why this is a thing, because it looks terribly awkward when the player is looking a different direction then what their body is facing. But come on, we should be able to do loops with the Elytra. That would be so sick. Wow, I just realized how long my bug report is, so Im going to finish.
If you read this far, thank you for reading all of it, and regardless of taking my recommendations into account or not, may you have happy programming.