If you are still having trouble with this here’s what I did on my 10.5 pro (so I’m sorry if you don’t have the things pro has):
- Select the midi track where the instrument changes from the one you want to the default setting every time you hit the “Stop” button on the transport bar.
- Go to “Midi” (right at the top) and select “Open List Editor”
- Delete all the Programme Change and Controllers at the top and
- That’s it. Your selected Halion Sonic sound should remain in place now.
I hope this helps!