Comment 8 for bug 587658

What you need to do is write down good instructions on how to reproduce.
You need to figure out whether this is a protocol-specific issue (for example, it happens just with MSN clients sending to empathy) or a generic issue with all protocols.

dicorfu, try asking at forum.ubuntu-gr.org for help to diagnose, or the ubuntu-gr mailing list.

It appears that there might be some limit to the size of the text box of the chat.

Empathy bugs are recorded at https://bugzilla.gnome.org/browse.cgi?product=empathy
A quick look at the chat messages did not show something relevant to MSN.
You can try to search a bit more.