Loss of column formatting from plugin

I have an interesting situation. Please keep in mind the following scenario works fine with your plugin’s original method of using [insert_php] tags.

Here is the scenario: I have a WP page that is used with [insert_php] tags and the only thing it does is call a pure php file, like this:

include_once('wp/wp-includes/includes/webform.php');

The raw php page includes short codes for column formatting using a WP plugin. Now, when I create a snippet with the above code and then place the snippet shortcode in the WP page, the pure php is still called, but the column formatting is broken. The form displays but now all the column shortcodes are being shown as plain text on the page for all to see, amongst the form elements.

Happy to answer any questions. I doubt this is a routine way to accomplish the task at hand.