Yesterday, I checked another Windows 7 x86 system that's running Avast without the startup problem. Its aswbIDSAgent service was set to Manual but already running upon bootup every time. Maybe, that's bob3160's case. He did mention in an earlier post on this thread that he hasn't got the problem since installing the latest beta.
As for computers that can't start the service upon bootup for whatever reason, the Behavior Shield would be disabled. The solution for them, therefore, would be to set the service to Automatic.