Today I was pair programming with one of my co-workers, and during the session he somehow made Task Manager tile, menu bar, tabs, and status bar disappear. At first, we had no clue how it happened and were forced to use Alt+F4 to close Windows Task Manager because close (x) button was gone with the title bar. However, in a little while he did it again. He was double clicking on the empty space in the top border.
You can try it yourself. Just start Windows Task Manager and double click anywhere in the empty space in the top border. Double click again to get the menu and tabs back. If you are not sure where the top border is, just double click in the same place the cursor is located on the image that you see on the right.
If you know of other weird behaviors in Windows, please let me know.