User blog comment:DaNASCAT/Technical Update: November 6, 2012/@comment-166269-20121106200427/@comment-957747-20121108005105

In a nutshell, what Jazzi said is true. It was added accidentally but we had more users that were happy with the change than those that were upset about it... so it will now be a feature for Monobook users.

If you wish to hide it, you can use the code Jazzi posted in your personal CSS file.