Strange Button Behavior When USB DAC Connected

[Blake Seaman]

I just got the Fiio Kunlun E18 DAC/AMP and a micro-USB to USB-C cable and have been loving the performance with my Lumia 950! It is immediately recognized upon plugging in as an "External Monitor" and all sounds go out through it. There is one catch however: I lose control of my hardware buttons. For some reason once I turn on the DAC, the phone's power button either doesn't work, or takes screenshots, the volume rockers are dysfunctional, and even the software home button doesn't usually work.

Anyone have any ideas on why this is happening?