/tp -> facing giving inconsistent results in multiplayer

Release_478003

Summary:
When using the facing parameter in the /tp command, running the same command doesn't always result in the player facing the same direction.

Impact:
Getting players to face the correct direction won't work consistently. Not currently using this for a map, but it was discovered while attempting to diagnose a mob teleportation bug.

Repro Steps:
1. Start a multiplayer world.
2. Teleport yourself to a set of coordinates, and make yourself face a direction. "/tp @p x y z facing x2 y2 z2"
3. Note where you're facing, then move your cursor and run the command again.
4. Repeat step 3.

Observed results:
Player faces different spots when running the same command.

Expected results:
The player should face the same spot every time.

Screenshots/videos attached:
No