Cannot access Web Server from LAN when using its global IP address.

Hi,

I have a web server connected to my DMZ network.  The DMZ network is connected to the Fortigate. 

The web server is accessible from outside.

It's also accessible from LAN if I use the local IP address.

However, it's not accessible from LAN if I use the global IP address even though I can access Internet freely from the LAN.

How can I troubleshoot and fix this problem?