What I expected to happen was...:
The chat message should return as "Cannot send chat messages" instead of Crashing.
What actually happened was...:
I muted my chat, typed a command, I crashed.
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ... I went on my server.
3. ... Muted my chat.
4. ... Typed a command.
5. ... I crashed.
6. ... Tried doing it on a LAN World. Everything is fine.
Environment
OS: Windows 8 (ver 6.2, arch amd64)
Java: 1.7.0_25 (by Oracle Corporation)
Launcher: 1.0.6 (bootstrap 4)
Minecraft: 1.6.1 (updated Mon Jul 01 05:47:29 MDT 2013)
Based on a crash report provided in this issue, I believe with high certainty that this report may be a duplicate of MC-20163. You can view all information known about this specific crash at MCX-777.