Modifying app permisions breaks app build process

[joshas]

Checklist

• [X] I agree to follow the Code of Conduct that this project adheres to.
• [X] I have searched the issue tracker for a bug that matches the one I want to file, without success.

flatpak-builder version

1.4.1

Flatpak version

1.15.10

How to reproduce

1. Build flatpak application using flatpak-builder
2. Run application and notice, that it is displayed among "Background Apps" in GNOME system menu
3. Go into "Settings" -> "Apps" and remove "Run in Background" setting for this application.

Expected Behavior

Permissions should not interfere with application build.

Actual Behavior

flatpak-build stops with error message: clang++ "Child process exited with code 137"

Additional Information

If custom permission settings might interfere with build, flatpak builder should inform about that before build. If this is something by design, I would like to know explanation, why this happens, just to satisfy my curiosity :)