How can localhost cause display issues on my web page ?

Hi ,

I am using IIS V10 for Windows 10 . The issue I have is that when I use localhost in my URL there are display issues on my web page 

so this will give issues. If there are any html controls and they have a value they seem to come back as NaN0.0

http://localhost/test/default.aspx

But if I use the following 

http://fullwebservername/test/default.aspx 

there seems to be no issue.

Is there a mapping that I have not doen correctly ?

Thanks