If you think back to the security settings msn tested a few months ago, you might remember that they disabbled the spaces, and today button, and made song links unclickable.
Now what could be happening is the security settings have been applyied by region or user. This could be msn testing if the security changes make a difference, or they could feel the need to protect you
The only other thing that could remove the buttons is a patch, so make sure your using an unpatched version.
Is your search button also gone?
@Black stalion
What version of messnger plus are you using?
also have you tried turning the plus button on the contact list off (Preferences>>Contact list>>Uncheck "Enhance the contact list with pluses features") as this is the only thing that alters that part of the messenger window.
Also are you using any other patchs/add ons, or a skin?