This was also the case with minimized applications in Windows 95 and as such you could click below the box.
In Windows 98 they realized the mistake - but in a typical Microsoft way of solving things, instead of simply making the area clickable below they instead forced the mouse up by 2-3 pixels every time you decided to be so silly as to try and click below the box.
I believe there is a technical reason for that 2 pixel move. If I remember correctly, old 16 bits applications can receive mouse messages from minimized windows. They didn't want to break compatibility by posting out of bounds messages.
In Windows 98 they realized the mistake - but in a typical Microsoft way of solving things, instead of simply making the area clickable below they instead forced the mouse up by 2-3 pixels every time you decided to be so silly as to try and click below the box.