I can’t duplicate this. I have 1.4.4 installed on a test site, I’ve placed a template in my theme folder with the following at the top of the file, and I get the selector just fine when editing a post.
Single Post Template: Special Post Template
One thing you might try is clicking the “Screen Options” slide down tab at the top right of the edit post screen. Make sure you check the box that says “Single Post Template”.