Managing library directories too quickly can cause a deadlock on Flatpak builds

[Userwithaname]

I've so far only been able to reproduce this issue in Flatpak builds. It can be reproduced consistently using the following steps:

1. Have a few directories set in the library settings (they should contain song files)
2. Remove all directories by quickly pressing the 'x' button on the topmost directory until all of them are gone
3. Quickly start adding the same directories again (usually adding just one is enough)
4. Observe how Mellow no longer accepts any new directories being added, and may freeze with no way of closing

Afterwards, other Flatpak applications become unresponsive as well, and the only way to recover is by restarting the system. I am guessing a deadlock occurs somewhere, which somehow affects the Flatpak file permissions portal? Since the application cannot even be force-quit, I wonder if a deadlock is happening within the portal itself.