It's kinda funny that the thread I found is pointing you back to your own post!
Now I know for sure I'm really going in circles.
I wonder if the "disabled check-box" is a new feature or a bug in Outlook 2013...
The only other thing I can think of is, if you are using a Standard Account when setting up the email, try temporarily making the account an Administrator and see if the TEST check-box can be disabled.
I know that's a long shot, but I've seen where some programs / settings don't work correctly with a Standard account.
I have Outlook 2010 and don't have Outlook 2013, so I can't play around with this.