I seem to be experiencing some issues with the folder management system.
Subfolder creation seems to be impossible.
Oh well, I guess I'll just have to put all of them at the top level.

3498899
I've found that a bug prevents an admin from creating a folder within a parent folder, but it's relatively easy to work around that. After the folder has been created as a standalone you can place it within its parent folder without any further problems.

3498988 Good to know, thanks!