I must say, this is a little confusing because an active region limits the output of the export to the active region.  Thus, the output of a single subtree misled me to believe that the "scope" of the export had been already limited to "Subtree."

I now see the variable org-export-initial-scope, but that's a little too heavy handed (since one can't export the entire file if it is left set to Subtree.  It would be nice if there was some way to have 'C-c @' automatically (and temporarily) set this variable to Subtree until the next export or until the region is de-activated.

Thanks again,

Dan