Navigation menu blank at first login in Joomla when extension is enabled

When you login on the Joomla backend and click CiviCRM, the navigation menu is blank (except for the search box) if any extensions are installed. Reloading the page in your browser makes it appear. You can see this in action at http://joomla.demo.civicrm.org/administrator
This happens every time a user logs in.

Disabling all extensions makes it work fine. This happened with a custom extension I wrote for a client, and I found the same thing happened with the CiviEvent Discount extension.

I'm not sure if this relates to CRM-11091 or CRM-10705, but it seems that it might.