It's not a big problem but it can be quite annoying at times. People can speak to me on msn without me adding them, when they speak to me it says "this user is not added to your contact list". If they spam or anything which a lot of them often do then I have to add them then block them, why is it people can speak to me without me adding them?
Have you recently mass deleted some of your contacts? If so they still have you added while you don't. Just do what you're doing now and add then block them. If not, just uninstall msn then re-install.