Directional light's real-time hard shadows not working with Intel HD Graphics 4600

I am using Unity Free 4.6.0f3 on a PC running Windows 8.1. The real-time hard shadows cast from directional light do not show up in either the editor's preview (both Scene and Game window) or the published web/stand-alone versions when I use Intel HD Graphics 4600 to render. However, the shadows do show up in all of the above cases when I use my NVIDIA GeForce GTX 780M to render.

I tried to tweak the Quality Settings in the Intel HD Graphics Control Panel, but to no avail. I made sure I had the newest version of Intel HD Graphics 4600's driver, 10.18.10.3960 as of today, 12/7/2014, dated 9/29/2014.

The shadows in the live demos from http://unity3d.com/showcase/live-demos do show up correctly though, even if I was using Intel HD Graphics 4600 to render, which makes me wonder what am I missing here.