It seems that the Chat (guild and friends) has an issue with the input validation. You can see this by doing things like
[sub]Test[-sub]
[b]Test[-b]
[FF0000]Test
[80]Test
All of them will applying formatting, but there is a \ inserted. This can be seen by sending a [ in the chat, it will always be changed to \[. This inserted backslash does not escape the formatting, it just adds the backslash to the message. If this is fixed, the developer fixing it may want to look at the code for NGUIText (function ParseSymbol is relevant)
