NEX-6 w/ ADP-MAA (hot shoe adapter) and HVL-F20AM (flash)

The flash works any mode as long as you turn it on (flip it up!)

The only issue is that--like the built-in flash--the camera likes to go at a higher ISO than it should in P mode--sometimes as high as 1600

My recommended settings are to use Manual mode and set 1/60 and iso 100-200, depending on lighting conditions for indoor use, and have flash exposure compensation at 0 to +.7.