Further update. Please help!
Tim Hunt suggested I manually create an editingteacher account ('test001') and manually assign the editingteacher role to this account for the course in question. I did so but unfortunately this account was also unable to see the course after login!
I am attaching the XML output that shows both the new test account and the original instructor account are indeed editingteachers in the course. I have also determined through the course's administration ("Assign roles") interface that Moodle sees the two accounts as "Teachers (editing)" and that in general (Users>Permissions>Define Roles) the Teacher (editing) role has the capability "View hidden courses".
Has anyone experienced this with Moodle 1.9.3 Build 20081224? I am virtually certain that I did not have this problem with earlier releases/builds of 1.9.3. Is this possibly a bug in the 24 Dec build?
Thanks for any help.