I don't understand what you are talking about. What do you mean by
URL's generated by VM itself?
When proving us a URL, don't just tell your domain name. Provide the exact URL where the problem occurs.
I am seeing this URL right now:
www.vipsfashion.nl/slippers/ which is the "Slippers VM Category -- OFFICIAL VM Category"
And the
SLIPPERS MIX RIVER product shows the "Choose Product Variant First" dropdown, because that product has "Custom Fields".. so what is the problem?
regards.