msmcleod - thanks for the insights. Yes, if I had known about that and assigned the the TouchDAW Master fader to Sonar master faders, I would have seen the problem much sooner.
I really would like to be able to use TouchDAW with Sonar because I record a lot of tracks alone (and it usually takes me a bunch of takes to get what I want). But since I posted about this problem I have had constant problems with Sonar locking up or stuttering or audio completely dropping out. After my initial discovery, I deleted and added a new Control Surface instance for TouchDAW. When I deleted that new one, Sonar started behaving again.
Do you have any ideas about other settings that might be tripping up Sonar, even when the Android device is turned off?