Mariette,  selecting any folder in the filemanager and clicking synchronize will refresh back to the root folder with no changes.   Selecting any folder (after renaming a file or folder on the server side) and selecting recursive synch will refresh to the root folder but then will show the old folder name and the new one.  Old folder will still show all files but if you select delete it will tell you that the objects have already been deleted.

I have the same problem.

An easy solution until fix is to go into the sql database and removing the folders and files manually