[otrs] Problem with refresh of overview page

Hi, We are running OTRS 3.2.8 on a virtualized (Hyper-V) Centos 6.2 server. We provided the vm with 4GB Ram. Ticket load is now ~50 open tickets. We have a strange problem that if we close a ticket and we return to the overview page, the ticket is still there. If we hit F5 a couple of times it will disappear. The performance of OTRS is good, we do not have any other 'lag' problems. Can we do anything about this? Thanks, Michel