Access Policy: view/edit file tree

Hi,
I followed the instructions at http://rtfm.modx.com/display/revolution20/Giving+a+User+Manager+Access to create custom access for an editor, who has to have access to resources and files, but not to any elements like chunks, snippets en templates.

Everthing works, with one exception.
The files tab at the left of the UI is visible, but only the top directory is shown, subdirectories are hidden. Trying to upload stuff fails, due to "access denied". Creating directories and uploading files seems to work (they’re visible with an admin account), but are not shown under the editors account.
I checked the following permissions in the access policy manager:
file_list, file_manager, file_remove, file_tree, file_update, file_upload and file_view (among others).
Where’s the catch?

Thanks in advance for your kind assistance!

I compared the permission settings with the ones I applied to an editor account in another website where traversing the filetree does work.
They turned out to be the same, so I guess permission settings are not to blame for this behavior.
Both sites use version 2.0.8-pl on the same LAMP-stack.

Could anyone point me in the right direction, please?

Thanks!