Breaks custom taxonomies

In the function my_theme_redirect() your plug-in includes your plug-ins template if is_tax() returns true – which it does for any category.

It should be is_tax( 'wpccategories' ).

Also, just as a heads up, template_include (filters the template file) should be used here instead of template_redirect (see this post: http://wordpress.stackexchange.com/a/51041/9364 ).

Thanks for your time!
Stephen

http://wordpress.org/extend/plugins/wp-catalogue/