Space Above Window When Maximized

I bought myself a new laptop recently and it arrived today. When I maximize a Window, it sometimes leaves space above the window. It is very, very noticeable, at about half a centimeter in height. It doesn't always happen, but when it does, it is only fixed by logging off and back on again, and even then it is only temporarily fixed. If I put my computer onto standby and then bring it back on, the problem is often created, but sometimes it just happens if I launch a program. The link below goes to a screenshot showing the problem. It leaves space above my window and in that space my desktop is visible. [URL].