The Bug:

Signs and hanging signs destroyed within spawn protection don't retain their contents for the client.

Steps to Reproduce:

1. Start a server, join it, give operator permissions to yourself, and switch into creative mode.
2. Set the world spawn to your current location by using the command provided below.

   /setworldspawn ~ ~ ~

3. Obtain a sign, place it down, and write some text on it.
4. Remove your operator permissions, and grant anyone else with them in order to activate spawn protection.
5. Break the sign that you just previously placed and observe its contents.
6. Take note as to whether or not signs and hanging signs destroyed within spawn protection retain their contents for the client.

Observed Behavior:

Signs and hanging signs appear empty for the client.

Expected Behavior:

Signs and hanging signs would retain their contents for the client.

Code Analysis:

Code analysis by Marcono1234 can be found below.

The following is based on a decompiled version of Minecraft 1.11 using MCP 9.35 rc1.

The method net.minecraft.network.NetHandlerPlayServer.processPlayerDigging(CPacketPlayerDigging) sends a SPacketBlockChange when the player starts, aborts, or finishes breaking a block which they cannot destroy, but it doesn't send a tile entity packet if a tile entity is at that position, resulting in this problem occurring.