This feature just does not work and the support/doc about this is unexistent. So unless you are a good programmer, avoid virtue mart at all cost for even basic business with downloadable files.
The customer experience is even worse, they have to fill unecessary fields (you can remove a few, but not all of them, unless you go deeper in the code, otherwise you get bugs and no support). And the paypal redirection does not work well for languages.
The sales work fine though, but if you are into making a shop for downloadables, virtue mart is far from the best solution.