not much of a better explanation I think, Jim. What you said stands for a number of things in the main render window – only rendering all the frames will give you the results you expect. I think it has to do with Mograph effectors not really moving the clones except in ‘clone space’ but I don’t know the intricate details.
I do know with this setup if you turn off the vibrate tag (get rid of it) and let the clones move out under the effect of the effectors ☺ you get no trails at all in a picture viewer render since the clones haven’t really moved in the Tracer’s space (or something like that).
Also, you always play the timeline to get to a particular frame in the editor, I would guess, try jumping to a frame in the editor (just click on 50 in the timeline for example) — you get a mess the way it’s set up but that’s due to the Sweep having Constant Cross Section selected… deselect that and you get the same thing as in the Picture Viewer render, no trace if vibrate is deleted. If vibrate is there you get no traces in the editor but the same thing as before in the picture viewer – the spheres are out there with only a trace put there by the vibrate tag (I’m guessing).