Problem with 'ex_pages' parameter…

I am using “Ambrosite Next/Previous Page Link Plus” to navigate between lessons within tutorials I’ve written on my website (http://www.mrcruwys.com/wp/). It works perfectly within each tutorial, however, the main menu options (“Basic Tutorials“, “Medium Tutorials“, etc…) have a “previous” link when I’ve listed them in the “ex_pages” parameter. I can’t work out why they are having a “previous” link generated when the opening page of each tutorial is having it excluded as expected?!?

http://ww.wp.xz.cn/extend/plugins/ambrosite-nextprevious-page-link-plus/