Ok, we checked the problems. When we use the most recent version of the Easy digital downloads plugin we have the same problem you described in your first post. We checked our files, but we did exactly what the found recommended to hook into the plugin. In our demo we used an older version of the plugin (2.9.8), with this version it working without any problem.
We checked also the problem from your second post, but no matter what we try, we can edit the page with the shortcode. Do you think you can send us ( info @ 7theme. net ) a login for your website, then we can check it in your admin panel and help you to solve the problem.