Midi keyboard playing tenor voice when keys are pressed

My score has a Tenor and Grand Staff.

What works:
Everything plays the way it should when I play the score. Notes sound correctly on each staff when click on them with a mouse. When I am in note entry mode and press any key on my midi keyboard they play the appropriate piano note correctly.

What does not work:
If I am not in note entry mode, and press any key on my midi keyboard, they play the corresponding tenor voice note, not the piano note.

I have dug around in the mixer and in the staff/part properties, and have gotten nowhere.
I have attached a piece of my score.

Thanks for any help.
SW