When hovering over a user's avatar, a menu is displayed containing three options: "View user's profile", "User's public repos" and "Send message". Before the Altassian branding was applied to the site, the menu was displayed on the right of the avatar, and moving the mouse over to it was possible.
In the new branding, the menu is displayed below the avatar. Attempting to use the menu by moving the mouse over to it results in the menu disappearing, presumably because the menu responds to a mouseout event fired by the avatar. This makes the menu impossible to use.