I have similar problem, but it's far smaller.
When I review the log of MP!L, I found that the first sentence of the last chat is lost, I'm sure because I can see that in the chat log of the ML! itself.
I am using Win2003 Enterprise SP1 Chinese Traditional.
The version of ML! is 8.0.0792.00, and MP!L is 4.0.0.235.
What's the cause?