I am working on a Wordpress-based project, and I just added a new template to the installation by uploading a template file. I was creating a new page that will use my new templ
I had the exact same problem with WordPress 3.2.1. I added a new template and the menu disappeared from the page add/edit screen. The solution was to switch back to the default twentyeleven theme end then right back to my custom theme. The templates drop-down began appearing again.
BTW, you said "revert to the default template, and back to my custom template" but I'm pretty sure you meant theme. I'm guessing where you saw this was here:
http://wordpress.org/support/topic/template-file-drop-down-not-appearing
Looks like this bug has existed for a couple of years at least. I filed a report: http://core.trac.wordpress.org/ticket/18324