Hi,
SEF URLs are always headache. Because sometimes, links get new itemID because of the page you are visiting at that time, therefore their SEF URL's gets changed.
The best way would be assigning a menu item for each links. Therefore the "Menu manager" will decide which SEF should get those links. So regardless of the current page's itemID, those links will have the constant itemID (because you are defining one them already by creating a menu item for them) so they will have always the same SEF URL.
Another possible confusion would be because of this;
Due to the structure of Virtuemart (this is not a bug though, this is the normal way). Lets say you have 2 categories: Jeans and Tshirt. And you have Diesel manufacturer.
If you are in the Jeans category and click the Diesel manufacturer. You will see Jeans from Diesel manufacturer. Not Jeans+Tshirt from Diesel manufacturer.
Understand what i am saying? Maybe the empty page you are seeing is related to that. But define "empty page". Is it completely empty, which is a 500 Internal Server Error? or everything is fine, no PHP error, but there is no product found in the Virtuemart.
Regards.
Support & Development