Hi, my question concerns hdmi arc and hdmi mhl ports. 
I have my beam connected through the hdmi arc port as specified and it works fine. 
I tried to add a Chromecast dongle type thing to the hdmi mhl port (as it was the only free hdmi available), and it stopped the arc port from working. 
Disconnecting from the mhl port lets the arc kick in again, and the beam works as expected. 
Any idea why mhl should override the arc hdmi input?

thanks in advance.