Are both rollers making contact at all times? Perhaps at the switch they are both for a short period off contact that is only manifesting itself as an issue at slower speeds. If your lucky, that will be your problem. My issue is with my Fast Track track that allows the unhooking and such. On my vintage engines I get the same problem you have, engine goes over it and it switches the e unit to neutral and I know it is making contact. So yours could be too. Newer engines from the late 70's don't have that issue. So there could be some kind of issue with the e units thinking they are having the voltage shut off when they are not on these older units. Don't understand how it can happen but you and I seem to have a similar problem.

Larry, locking the e-unit is not a "fix" for this problem as the e-unit was/is a design function for these trains. If there was an "interruption of power" it would not elect what vintage the engine was to interrupt yet we both have this issue with the vintage engines, not, in my case, with the more modern engines even thought they have the same pickups as the older version. Yes, I bandage the problem by doing what you suggest but again, it is a bandage that does not allow use of the full features the engine offers. I've had this happen when using my whistle at times too on these older engines. It almost seems like something happens to the current at some of these track junctions or use of electrical functions which fakes the early (or perhaps more worn) e unit into thinking there was a power interruption.

That still does not answer why, at times, when I use my whistle function, the e unit will cycle too. There is no specific piece of track it happens on, it just happens here or there randomly. Any idea what causes the e unit to cycle then? Yes, the whistle does function when this happens.