Well an hour and a cup of coffee later an I have figured it out:
1. Open kses.php in your favorite text editor
2. Find the following block of code
// Post filtering
#add_filter('content_save_pre', 'wp_filter_post_kses');
#add_filter('excerpt_save_pre', 'wp_filter_post_kses');
#add_filter('content_filtered_save_pre', 'wp_filter_post_kses');
3. Comment out the lines as show and save, then all is well.
I am learning PHP so I think I may attempt to write a plugin to disable this.