analog video source available?
For instance, if there is a DVD player or VHS deck around... instead of connecting the camcorder to the ADVC110, connect this other video source and see if FCP X has an issue or not. If there is no rolling, then you're right, it is somehow the camera - I still can't figure out how this would happen with the step through analog land). If there is rolling, then it is either the ADVC110 or the Mac - but since it happens with FCP X and iMovie, I don't think it is either of those applications... It is something they both use. In this case, maybe a shared codec library or the ADVC110.