The hotfix can be downloaded/requested from the following link. The hotfix is available for both AX 2012 and AX 2012 R2.
Like all the other hotfixes to the product binaries, it's a full service roll up of hotfixes to all the binaries.
The core of the fix is that a performance optimization for the address bar has been authored that is more conservative about the amount of information it requests. This optimization would be beneficial for organizations who manage multiple companies within Dynamics.
Specifically, every time the address bar was used to navigate to a list page, the address bar would ask the system for a list of companies to display – under the assumption that the list of companies may have changed. With this optimization, the company list is requested once, and used throughout the session. If a company is added while a session is active, the user will need to explicitly refresh the list by clicking the refresh button on the address bar, or by logging off and back into Dynamics.