Whether it differs by one byte or one million, it's still hacked
It's not that the topic needs locking or anything, just that we can't troubleshoot a problem that's being experienced on software that shouldn't be used.
I experienced a similar problem on aMSN for Mac but never managed to do anything about it, I just stopped using it and used WebMessenger instead.
The best I can suggest is to upgrade to the latest stable and supported version of WLM 2009 (or the 2010 beta if you'd prefer) and then if the problem persists you may be able to find some help for it