Currently, the standard payment plugin returns plain html as a response to a confirmed order. I would propose a new solution in which the plugin responses by a redirect to the virtuemart pluginresponse view.
In the attachement, I added standard.php in which the idea is indicated in function plgVmConfirmedOrder. Note that the virtuemart version of the example is vm 2.0.10, however, I've checked that my issue still applies in the current version.
[attachment cleanup by admin]