This a usability problem with the current implementation. Click the sound volume menu-like thing using Fitt's law and pointing at the top of the icon. Now try to move the mouse in a straight line from the icon to the right-most end point of the volume slider (see attached illustration). The menu-like thing closes and opens the letter icon menu instead because the mouse crosses the letter icon on it's way towards the slider.
Interestingly I can see the Program/Places/System menus have the same issue. It's probably much less likely to occur there because those are are actually menus, so you don't need any horizontal movement.
One way to fix it would be some kind of intension guesser - so maybe measure the velocity and add a bit of timeout? There's a Javascript thing that does something like that:
http://cherne.net/brian/resources/jquery.hoverIntent.html
Hi Conor, I think the duplicate status is wrong.
Bug 538493 is about a problem that happens inside the sound indicator.
If you reread my report, this bug is about something that happens outside it, namely that a different menu is pulled down. This has something to do with the (broken) design of the whole indicator menu system, the only reason why I mention it for the volume control is that it's probably more of a problem here because it has a horizontal layout.
Could you please unduplicate it? :)