I'm happy you found a workaround, but would you be willing to use the "Report A Forum Bug" link in the right column to report this missing checkbox issue with the default & Minimalist themes to Reggie, the Talk admin?

If you find it to be too much trouble, just say so, and I'll report it for you. I just have this evil plot wherein I try to get people more involved in all aspects of the community, bug reporting included.