I also apologize for exhuming this old post, but this is no solution. I'm using Civil 3D 2008, and my "Paper/Model" button is also constantly turning itself off. I don't think this habitual loss of the "Paper/Model" button was mentioned in the post, but I believe it is the main reason some of us are looking for this button in the first place. The button was always visible in previous versions of AutoCAD flavors. I appreciate the fix that was mentioned in this post. I did not know that I could click on the black arrow to get the list of status bar buttons. I've been right-clicking on the razor thin space between the buttons to get this list. It's tricky, but I've gotten good at it. Now I can easily click on the arrow. Yes!
My obtuse work-around aside, my main concern is that this problem still isn't resolved. Why was the button off in the first place? Why do I have to keep second guessing myself in every new version of AutoCAD? Why does my "Paper/Model" button stay on for a while, and then one day, mysteriously turn off, forcing me to go down there and turn it back on? I'm always doing this. Why, why, why? Should this problem be elevated to Autodesk, or am I kidding myself to think that they should care about the consistency of their products' GUI?
Does anyone know of an AutoCAD system variable that I can put in a LISP to turn this thing on ever single stinking time that I start AutoCAD. Apparently Autodesk can't do it right, so I'll fix it myself. Anyone want to help me, this bitter Civil 3D user?