I read the post
www.artio.net/support-forums/joomsef/cus...hNjETCvKcfiCyNOvb-Rg
Also in my site this behavior is not due to the enabling/disabling JoomSEF extension Virtuemart, but only for JoomSEF Extension 4.4.0.
"Using the Script ajax Countries / Regions" is checked in VirtueMart backend.
I tried to change the values of "Set page base href value", deleting and regenerating-sef url, but the problem is still there:
Regions/States dropdown list does not autopopulate in VirtueMart frontend (i.e. the Regions/States dropdown list is empty).