Sam Gentile asks, "Why do titles that have been set in Radio and inserted manually into the Item Template not show up on any category pages even if they use the same exact template?"
Categories each use their own copy of a theme's template files (including the item template). When you choose a theme for a category, Radio puts the theme's template files in that category's folder in www/categories.
Or don't set themes for the categories. They'll inherit all the templates from the parent directory.
Thanks for the tip.