Ciao,
thanks for answer. At the same time I'm working on another website with vituemart and custom fields.
In that website we have no problems even though products are published with custom fields so i supose the issue is not related to the virtuemart files.
I switched on protostar template on that site for further check and it works fine too, you can see screenshot.
I need a few days to test and find out where the problem might be and I ask you not to close this ticket for now.