In the file manager, if the name of a folder ends with a dot (.), the folder cannot be deleted. No error is generated, but the folder is not removed, and the current directory is changed to "Files/undefined".

To reproduce :

• go to any place where files can be managed (file, folder, etc.)
• create a folder with any name, e.g. "test" (if you put a dot at the end here, it will be removed)
• rename the folder, putting a dot at the end, i.e. "test."
• try to delete the folder : the folder cannot be deleted
  If you rename the folder again, removing the dot, you can delete it

(I didn't deliberately create folder names ending with a dot. The problem appeared when I imported some backups from Moodle 1.9. When I tried to delete all the files and folders in "Legacy files", I couldn't delete the folders having a dot at the end of their name).