Paolo,
So many thanks for the quick response!
WP permalink are indeed set to include the %/postname/%, but I found out what the root cause was. You may find this interesting. My site was a one-click MOJO install, from bluehost. I whipped it all off and built a side from scratch downloading wordpress on my own. Problem gone. Some kind of compatibility problem with one of MOJO’s plugins, I’m sure.
Many thanks once again!
Damian