@Ron
Ron, thanks for your idea. I just tried this to my fluid grid css file, and it worked! The odd thing (at least in my mind) is that the code (shown below) is commented out. So, even though my web pages ignore this commented out code, Dreamweaver does not... it uses it to control how the Dreamweaver program operates. Well, I guess that this can happen. This code acts like a "directive" to the Dreamweaver program.
One noticeable change is that in Live view I no longer see the grey strips showing the fluid grid columns, but I can live with this.
This is my novice way of looking at the situation. But now I am happy.
Here's my exact code (that I deleted) from my css file. Maybe others can try this and see if it fixes the problem.
/*
Dreamweaver Fluid Grid Properties
----------------------------------
dw-num-cols-mobile: 4;
dw-num-cols-tablet: 8;
dw-num-cols-desktop: 12;
dw-gutter-percentage: 15;
Inspiration from "Responsive Web Design" by Ethan Marcotte
http://www.alistapart.com/articles/responsive-web-design
and Golden Grid System by Joni Korpi
*/