Odd switch malfunction

Correction:  The offending switch is a Lionel 6-16829 RH Command/Control switch.  Sorry!

Do you have the fork that does not switch have  an isolator pin installed?

Thanks for the replies guys.  I did a little more troubleshooting today.  The switch would not auto switch when running my MTH E8 (A unit only).  However it acted normally when my Lionel Berkshire ran through it.  Very odd indeed.  I wonder if it has anything to do with the spacing of the pickup rollers?...

It's the outside rails that do the non-derailing function.  This isn't a newer MTH that has a 2-rail/3-rail switch, is it?  Could that be the problem and it's insulated one side of the wheels on the trucks?

Well, I wouldn't call her modern by any stretch.  It is an MTH PS1 ABA from 2000.  

I just completed some bus and feeder work John.  It doesn't matter which rail you connect ground to does it?  I always try to use the outside rail, but due to my layout, that was not always possible with the Fastrack.  I can't see how that could be the problem as the grounds are tied together on each track section with a bus bar.  Oh, and the switches are not fed directly from the feeders, due to building constraints (hardwood floor crossover) but are fed with ample power from 4 sides.

Sounds like some internal issue with the switch.  It's the wheels that trigger the non-derailing function, does it work with all other locomotives?