Minor update

Please add the following line:

$args = apply_filters( 'wp_terms_checklist_args', $args, $post_id );

to your code of mfields_terms_radiolist() forked from wp_terms_checklist(), after line 231 in radio-button-categories.php, so themes and other plugins may alter function arguments (for switching to hierarchial output mode, for example).

http://wordpress.org/plugins/category-radio-buttons/