Newly rendered players always look south until they move their head

The bug

When another player is newly rendered on a server (e.g. joining in the server, getting in your render distance (MC-130411), or respawning (MC-237037)), they will look south until they move their head. This can look pretty strange if the body of the player is facing, for example, north.

Steps to Reproduce

Get two players and label them, "Player A" and "Player B".

• Let player A enter.
• Let player B enter.
• Let player A face north.
• Let player B move far away (beyond render distance) and back.

Observed Behavior

"Player B" sees "Player A" now facing south when actually "Player A" is still facing north, therefore indicating that when newly rendered by the client, all players appear to be facing south until they adjust their head rotation.

Expected Behavior

The expected behavior would be that when players get rendered, all players would appear to be facing the correct direction.

Code Analysis

The following is based on a decompiled version of Minecraft 1.10 using MCP 9.30.

It looks like the method net.minecraft.entity.Entity.setPositionAndRotation(double, double, double, float, float) which is called when a player is spawned client-side only sets the body rotation. This could be fixed as well by sending a net.minecraft.network.play.server.SPacketEntityHeadLook.SPacketEntityHeadLook(Entity, byte) packet after the spawn packet.