Hello again.
rharv, I deleted the StaffCTRL entries in the Event List; it made no difference. I still got piano.
Jeff, The forum doesn't permit SEQ files to be posted, so I uploaded them here:

https://1drv.ms/u/s!AgX4ohRdkH5xhfYUl-hj7Kz0VqGofQ?e=btcsYx

Please cut and paste the link into your browser.

There are 2 files; a simple C Major scale where, in PT, I specified the Casio patch for GM Organ 1. I get piano sound when I play this back using the Casio keyboard. I then saved it as a MID file, used a media player to listen to it and it played back as Organ. Then, as an experiment, I converted the track to a WAV file in PT and it played back as Organ too. I didn't bother to upload this file.

So, it seems that PT is doing what is necessary to use the right instrument. My keyboard is obviously the problem. Still trying to figure it out...

Thanks to you both.

Barry