Products don't appear in category

[pensieristupendi]

I have a problem with products.
I just update joomla and virtuemart, so they are updated.
When I open a category, I cannot see all the products but just a part. There isn't any limit for products to show and if a add a new product, the sistem show me another product apparentrly without any logic.
Anuone has ever had the same problem?