What Raymoh says sounds familiar to me, and a temporary stop might be a good idea. I never wait for the (normal) preview to finish and make all sorts of adjustments and usually all goes well, but ocassionally when doing a simple change TG crashes. With RT preview I am more careful, hardly ever have it on when doing changes, except on clouds, as I found it more prone to crashes.
On another note, preview restarts also after changing the size of the crop; is that necessary?