On most of the soundtracks that include DD-EX that I've played, the flag triggers the 6.1 processing automatically at the beginning of the movie. I don't have a 6.1 setup, but tell my 1050 that I do. This way the sound will not drop out as the flag keeps trying to activate the processing.

I've only had one case where I could deactivate the 6.1 after being activated by the DVD, and have it remain off.