Well, there’s a big problem with Flatpak, then. A user who wants an application shouldn’t have to comprehensively research the corner cases of a platform before using it. It’s enough to make you just go buy a Mac 
I don’t mean to pick on you here, after all, you solved my problem! 
I’m just pointing out a new-user hazard. Worse, that new user is unlikely to think the issue is in flatpak, but in RT – I wonder how many problem reports they’ve already received and scratched their heads over, when the problem’s outside the scope of their influence?