a reboot unfortunately does not help.
i think the thing with the installer is only coincidence, i actually think the apps you have open don't have any relation to this bug. it happened to me on several apps now...
by the way this is not always the case. 90% of the time mission control works just fine...
furthermore, it's impossible to predict when this bug will uccur or not.
I think it happens when there is a dialogue box that needs to be selected yet never does and then you moved onto a different app. There is a slight catch where mission control will not show some of the pop up windows in it's view. only when you go to that app does it do it.
might want to do a PRAM reset?