SD40-2 that will not turn off horn and crew talk in lash up

One thing I found is sometimes you need to turn off the crew talk and horn on the lead unit and let the trailing unit do the crew talk.

I don’t know if this is the problem, but I have a Lionel SD40T-2 built about the same year (6-38937).  To avoid having the horn and crew talk activate when it is a trailing unit I can do one of two things:  1.  Assign the train number to be less than 10 or  2.  Run it as a trailing unit in the same direction as the lead unit.  If I use a train ID above 9 or try to run it as a trailing unit whose direction is reversed relative to the lead unit, I get the horn and crew talk from both it and the lead unit.

Interesting.   I will note that I was able to put unit 957 in the tail end and turn off horn and crew with train 95.  I hope Dave can shed some light on it.