[Nav-users] Port description not updated

My NAV installation don't update port description. I'm using switches Cisco Catalyst 3750: Cisco IOS Software, C3750E Software (C3750E-UNIVERSALK9-M), Version 15.2(4)E, RELEASE SOFTWARE (fc2) I already had this problem, I also updated to the latest NAV 5.13.1 but I always the same problem. If I change the interface description from NAV GUI (portadmin), description is not updated on the switch. If I change, for example, vlan, vlan is correctly updated. Any suggestion will be appreciated. Davide