I think you dont understand.
I dont said it's not a bug, but that the "no override" is only in Virtuemart, because the VM core team do not use Joomla layout, but have done own way to check layouts using VirtueMartModelConfig::getLayoutList
If you have for eg. a layout in the non default template, Virtuemart do not find it, because the code is :
$q = 'SELECT `template` FROM `#__template_styles` WHERE `client_id` ="0" AND `home`="1" ';
$db = JFactory::getDBO();
$db->setQuery($q);
$tplnames = $db->loadResult();
And only load 1 template, the default.
And add a "no overidde' option.
Check any other modules that is not from VM team.
You get always all templates and never "no overides", because "no overides" is a logical error for joomla modules.
So yes, its bugged and yes it's limited, but this bug and option should not exist.
You understand better ?