My AC Scout engine runs both forward and reverse on my DC powered track, just by interrupting the DC power supply leads.

Unless you have one of the very few DC starter sets, your locomotive is designed for AC power and uses a specialized latching relay (e-unit) that is either "2 position" F-R-F or "3 position" F-N-R-N-F operation. As you discovered, the latching relay position changes upon power interruption.

That's what it is supposed to do.

It's not an AC motor. It's a series wound universal motor. It runs on AC or DC.

Thanks.  I knew from experience from running engines on AC track that they would change direction when the power was cut, but I was really surprised that they would also do this when DC was supplied to the track.  I didn't think that the 3 position switch on the top of the engine would function properly on DC current.

Mannyrock

"Only the whistle is effected" on AC trains.  I suspected you'd missed that, but you were already on a new tangent. I knew you'd figure it out. 

I also came across an article on running on dc; this one suggested a piece of more durable mylar tape on the land/stop to prevent the eunit coil slug from becoming magnetized and sticking. 

Thanks, I knew the AC whistle tender would not work on the track.   But, this layout is for the kids.  So, to have a whistle, I am going to park a whistle tender on a piece of track, run AC to that track, and install a momentary on-off switch to blow the whistle.

On a small layout, they wont know that the sound isn't coming from the moving train's hollow tender.

Thanks

Mannyrock