Many of my steam games seem to not even be able to open when the overlay for mumble is active. I've tried disabling Steam overlay and had the same issue. Dota 2 is one example, my user icon will change to a green border saying I'm joining a game then it will go back to blue and Dota 2 or the game itself will not start. I have tried adding some of the launch properties but no luck.
The games that do start will not allow me to use the overlay. The overlay also does not show up in Battlefield 3.
I am running windows 8.