I'm not sure if this is what adresses the problem. But I read on the forums that when one person has WLM and MP!L and uses the code format like you do ( [ b ], [c=10] etc ), and when the other person does not have WLM and MP!L, it doesn't work.
I reccomend changing your settings. In the MP!L Preferences screen, on the last tab, you can change settings from BBCode to IRC. That might solve the problem. (Maybe you need to create your screenname again using the new code, I'm not sure)
If it doesn't solve your problem, I'm sorry. At least it bumped your post to the top of the list
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