For a long time now i've been using the latest stable version of Mumble and it was working great. 1-2 days ago i installed the 1.2.3 RC2 of Mumble and since then, games get random freeze ups every few seconds if overlay is enabled. Every few seconds (randomly) the game freezes up for 1 to 3 seconds. That only happens with 1.2.3 RC2, it didn't happen for all this time i have been using the stable client.
I tried altering the overlay settings and make them exactly the same like they were with 1.2.2 (without the black background box on the user names) and it didn't help. The only thing that helps is disabling overlay completely.
I don't know if it helps but i also have a Logitech G-15 keyboard (blue lights). I also said that because some user in #mumble in IRC had the same problem in the past, and he had the same keyboard too.