I have a case where while you're viewing an additional mailbox in
Outlook using Categories view, the Navigation pane will update and
indicate that there are new unread messages however they won't show up
under the "None" category. A quick fix for this issue is to go to the
primary mailbox of the Outlook profile and then go back into the
additional mailbox, however that's rather inconvenient. The problem at
this time is not reproducible, it comes and goes. Issue never occurs if
using views other than Categories. Is anyone aware of a fix for this
issue? Below are details on the environment/setup.

Outlook 2010 14.0.7140.5002 32-bit (Also tried Outlook 2013)

Cached mode is disabled for both the
primary mailbox and the additional mailbox (issue remains even with
cached mode on)

Exchange 2010 SP3 CU6

Primary mailbox in Outlook profile works
perfectly fine. Secondary mailbox is a shared mailbox. Access is granted
to mailbox using a security group. The secondary mailbox is about 4GB
in size.