Listing Author drop down box

I purchased an am using directory theme for my domain http://www.woodworker.co.za
I used to be able to edit listings (spelling errors, add categorie etc) while keeping the author the same as the guy who actually did the item. Now whn I edit a listing I no longer have the drop down box for the author and it automatically makes me (gavinadmin) the author. I have a few users on the site and now I, as admin, cannot edit any listings without the author changing to me. Please help