Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
iOS 6 : Look At New Design / UI Changes
If any of you have used the iOS 6 developer beta you will be well aware that Apple has tweaked a few UI / Designs. We have decided to show you the main ones below. The new designs are being very closely compared to android like notification center was when Apple introduced it in iOS 5. All the new designs make the user believe a lot more has been upgrade in iOS 6 and will give a lot more people a different attitude towards certain tasks as the new designs have cleaned a lot of tasks up.