See the Changelog for list of features and fixes.
Reopen unclosed private chats from previous session
Submitted by TJT on Fri, 10/12/2012 - 18:32
It doesn't appear to be an option available. I find it's very useful on the original client. If you crash or have a power outage, those open chat windows are gone. There's also times when I'm not able to reply to somebody until several days later, so I like to keep them open. I know everything is still logged, but sometimes I forget who has sent me a message.