Steps to reproduce the issue:
- Open a MIDI part in Key Editor.
- Right click on the Toolbar, then make sure “Multiple Part Controls” is ON.
- Make sure “Show Part Borders” is ON.
- Deactivate “Multiple Part Controls” (Right click on Toolbar > Multiple Part Controls).
- Reopen Key Editor (close it, then open it again).
Result: the part borders are OFF.
If you have time, please fix this issue (if you consider it to be an issue). Thank you.