Frank, since the code you posted in post#55 starts by loading application_top.php and ends by loading application_bottom.php, I've got to assume that the script either runs under the admin or is stand-alone running from the root of your store-front.

The only thing that I can think of that might work is for that script to have its own auto-load "prefix" so that the one-page checkout doesn't interfere with that after-order script.

First, copy the file /includes/auto_loaders/config.core.php to a file named mvs.core.php in the same folder. Next, modify that script you posted, adding the following statement just prior to the require for the application_top.php script:
Code:
$loaderPrefix = 'mvs';
That will result in that script processing like the one-page checkout wasn't in the picture since its observer won't be loaded due to the change in that loader-prefix value.