Thank you for your response.
I am using X-Plane v11.11.
I cannot reproduce the error anymore.
I remember exactly what I did:
1. Update the existing Saab 340A to v1.5.
2. Run XP.
3. From the main menu, click "Settings". Flight has not been started yet at this moment.
4. You see the error.
So, the error is only visible upon the very first run since the update, and it disappears if you exit and run it again.