I'm running Windows Server 2012, and in some games (GW2, Planetside 2, Civilization 5), the overlay will never show up. It also won't show up in Firefox if I unblacklist firefox.exe. In League of Legends, the overlay will appear (and function) for a few seconds and then disappear while on the loading screen (it does this everytime).
I'm chalking it up to the problem being because it's Windows Server Edition, and something mumble relies on is missing, but the games don't crash, nor does mumble, and there is nothing in any log files I have found. I would like to continue using Win Server 2012, and the mumble overlay, so any help in finding the cause of the issue would be great :)
The teamspeak 3 overlay functions without any problems, but I'm not sure how the different the injection routines are between mumble and ts3. The games also run without a hitch at 80-100+ fps, just like they do in Win7.