I found something in changelog of version 4.50
quote:
Fixed: in some rare occasions after signing-in or after experiencing connection problems, the wrong status is displayed for some contacts in windows such as desktop contacts and tabbed chats. This fix applies to Windows Vista and above only.
It may be a similar problem and Vista users may not be able to reproduce this bug if they are using 4.50+. I am on XP currently and I cannot test it myself.
quote:
Originally posted by CookieRevised
However, this may actually be a problem with Windows Live Messenger itself, which maybe doesn't update the status properly if a contact gets deleted or added.
Can be. Because I opened a convo window with someone who is not in my list, then I added it by clicking on the link in the convo's info bar "Add this contact to your contact list." but the tab of the convo still displayed a grey buddy although Messenger shows it online after I added it.