1. Ensure at least one other program is running, with its window maximised.
2. Drag the orange square over the blue square.
3. Without releasing the mouse button, use Alt+Tab (or your system's equivalent) to switch to the other program, then back to this one.
4. Move the mouse around inside the black square. The orange square should not follow the mouse.
5. Release the mouse button over the white area inside the black square. The orange square should disappear, and the blue square should turn yellow.