In ‘Shape', press the ‘Shift' key to draw a square or circle.
In ‘Shape', select a square or circle and click and drag while holding down the ‘Shift' key. A square or circle will be drawn. But make sure that you keep holding the ‘Shift' key until dragging is finished. If you release the ‘Shift' key, the ratio of the square/circle will reflect the current cursor location.