The single button press ends the call, rather than muting/unmuting - is this the same issue that's noted on the product page under compatibility?
Samsung Galaxy S II, Samsung Captivate
Due to software conflicts, the Klipsch Control app is not fully compatible, specifically, the Klipsch S4A headset only supports voice control, call Answer and End functionality. Klipsch continues to work on an update to allow full functionality on these devices.