Video here:

https://youtu.be/ohIeKd8xPZg

 It's possible the dragon just started to move which caused the player to get hit. However, the player is below the dragon, it certainly isn't going in the player's direction and the player doesn't even seem to be touching the dragon.

As far as I'm aware, the dragon launching you so high up is also part of this bug as this wasn't present in older versions and doesn't correlate with the dragons movements as you'd expect it to.

This bug seems to have been around for a while and has in my experience been a fairly consistent issue.