cyberdyne - 1:55 pm on Jan 13, 2012 (gmt 0)
Having just done as you suggested, Google returned my robots.txt file for all three search terms.
I'm wondering if it has something to do with an entry in my .htaccess:
<Files ~ (403\.php|block\.php|robots\.txt)>
Allow from all
Perhaps I shouldn't have robots.txt in that list.