Hyperlinks with hardware IP address work, but identical link with loopback IP does not

We have been using a tool called ePublisher by WebWorks to build help documentation which then gets installed on a process control system for context sensitive help.  We used to use local machine IP addresses in our hyperlinks to the context sensitive help application, but we changed to using the loopback IP a couple of years ago so that the code in our application is IP independent.   This has worked wonderfully for us for quite a while.

2 example Hyperlinks, one in the old style (hardware IP) and one in the new style (loopback IP):
Successful:
http://192.168.1.1/ProductHelp/_en/Index.html?context=Product1&topic=ScreenName1
Successful:
http://127.0.0.1/ProductHelp/_en/Index.html?context=Product1&topic=ScreenName1

We recently added a new screen to our product, and have subsequently built some help documentation for that screen, but when we add the equivalent Hyperlink to that application, the link doesn't work:
Unsuccessful:
http://127.0.0.1/ProductHelp/_en/Index.html?context=Product1&topic=ScreenName2

First we confirmed that the loopback IP resolves properly (no reason it shouldn't, but just in case)
Successful:
http://127.0.0.1/ProductHelp/_en/Index.html?context=Product1&topic=ScreenName1

Then we checked that we have the proper hooks in the WebHelp application for the hyperlink by replacing the loopback IP with the hardware IP again:
Successful:
http://192.168.1.1/ProductHelp/_en/Index.html?context=Product1&topic=ScreenName2

I haven't the slightest clue where to check next to figure out what would be different between using the hardware IP vs the loopback IP in hyperlink that would cause it to fail, especially since the hardware vs loopback IP both work when pointing to a different page.