If this has already been identified or fixed just ignore me...
Windows 7 Pro
Sending XML data as a spark message causes the XML file that contains the chat history to stop being parsed at the comment containing the XML markup. History was still being appended correctly to the file, but could not be displayed.
*See attached picture* (The message board also encountered an error when posting this data.)
My chat history ended right before this comment even though there were hundreds of additional messages after this comment.
Removing the message body containing the markup caused the spark history to show correctly.