New Inbox refresh behaviour since upgrading to 6.5.1 client

After upgrading my client to 6.5.1 (server is 6.5 and so it the mail template) I have noticed that when pressing F9 in my inbox there is a change of behaviour. Client OS is Windows 2000 and Windows XP.

In the 6.5 client, it used to refresh the inbox instantly.

With 6.5.1 you now see the network activity lightning bolt flicker and the Connecting to server and Connected to Server comments flicker in the status bar. This takes about 1-2 seconds to complete.

It only seems to do this in the mail file, refreshing the People view in the NAB behaves as usual.

Anyone else notice this? Any idea what is going on?