If mumble is running then you try to start arma3 in normal way using desktop icon it goes through the initial part of loading then screen flickers and freezes with strange colourscheme - arma3 stops responding, at this stage it has loaded ~68Mb into memory.
I am running 2 30"(2560x1600) monitors with the game on 1 only. the screen colour change only occurs on the game monitor.
Without mumble running then game starts normally and I can then start mumble without any noticable effect except that, of course, I don't have the mumble overlay - suspect this may be problem with how game loads mumble overlay. {F17834}