Windows Seven is a feature that ensures that you recently opened items of a program as you see with your right mouse button click. Some people may find unpleasant, however, this in relation to privacy.

There is a very simple way to disable it.

Right-click the taskbar and click "Properties".
Click the tab "Start Menu"
Check "Store and display recently opened items in the Start menu and the taskbar.
Click "Ok"

A very simple tweak, but very useful if you do not want everyone in one glance you see last opened items.