I'm trying to figure out what setting is in place that's causing my
solution to go through a complete rebuild each time I open it.  

1.  Open solution.
2.  Select Build Solution from the menu.
3.  Build completes.
4.  Select Build Solution from the menu, says everything's up to date.
5.  Close solution.
6.  Open solution.
7.  Look in output directory and confirm objects are still there.
8.  Select Build Solution from the menu, a clean build is started.  

I don't think it's a dependency problem because ALL of the object
files are deleted before the build starts in step 8 above, which to me
indicates a Rebuild Solution command was issued.  Or perhaps a Clean
Solution command got issued just before the Build Solution command.
What might cause a Clean Solution or Rebuild Solution command to be
issued automatically, i.e. by something other than the user?

At first I thought someone had sneaked in and remapped my F7 key to
Rebuild Solution.

The only thing remotely unique about the solution was that I used
Configuration Manager to create it and told it to copy the settings
from another project in the solution.  I've done this with a dozen
other solutions and don't have the problem with them.

Ron