Using RT 3.8.1.
If I log into RT with a user who has permission to see some, but not all queues, then the queues I have the rights to see are correctly listed in the 'new ticket in' dropdown.
If I am then given the rights to see some more queues, although the rights have clearly taken effect (the 'RT at a glance' summaries now show tickets I couldn't see before), the queues do not appear in the 'new ticket in' dropdown until I delete my cookies for the RT server (or close my browser).