I found a workaround (kind off)
I use sh404sef. In Sh404sef -> "Configuration" -> "Extension configuration" -> "Virtuemart" you can define if you want to use the flypage extension in the url...or not. If 'no' is selected, the end of VM product urls look like this: ...category/productname.html (instead of ...category/productname/flypage.tpl.html) . This way, the vm product links in the NSP are working just fine. (If you do/change this for a live site. Don't forget tot setup 301 redirects for your productpages)
For me this ''workaround ' is not 100% ideal, because I want to use a custom extension for my urls. (different form flypage.tpl.html) So, I'm not using it and would like to know if there is a solution.