Hi Maxim,
Probably you need to have menu item for VM Categories (Top Level of VM Categories) in your 'MenĂº de usuario' menus.
I've tried that with a backup in localhost and doesn't work. I've deleted all categories and only one parent category to display products, select box number doesn't work. On the other hand, I've spent much time to sort the categories, nearly 10.000 products, is important to have a good menu item distribution and easily accesible.
Using cache is not welcome for VM also. BTW I wasn't able to test without cache cos I had only admin (not superadmin) access.
I know cache is not welcome for VM hehehe. I've had many problems with cache and VM but have been resolved. Incorrect select box number is not cache problem, I've tested.
Did you try on standard Joomla template?
I've changed to others templates like beez or atomic, the problem persists.
I changed the permissions, you now have super admin permission but be careful please, website is actually operating and I would not want to stop working page.
Regards.