I have several systems in which the player is teleported to an entity (via @e), and in many cases when this happens it rotates the character in some way for no reason. Specifically, when I teleport the west-facing player to a ThrownPotion, it will rotate him to face east, and vice-versa. Teleporting when facing north or south is fine. I've also noticed this to apply when teleporting to mobs, although the pattern of /tp's changing rotation seems to not be the same in those cases.