Debug VFS: sftpSetUserDirIsRoot=false setting was not working.
In Commons VFS2 UserDirIsRoot is default to true :
http://commons.apache.org/proper/commons-vfs/filesystems.html#SFTP
Bug fix thanks to F. Rosan
cf https://listes.esup-portail.org/sympa/arc/esup-utilisateurs/2014-05/msg00007.html