Dual Weilding doesn't work on Mac

I was testing the latest version of the Snapshot, 15w32c, on creative mode and I found that dual wielding does not work as it should. When I'm holding a sword on my right hand and a bow on my left hand (With arrows on my inventory) and press the right button or "action" button on my mouse the bow will not fire and, instead, the sword will block. The same problem happens on Survival mode.