Host fails to read NTFS folder which is mounted to some partition

[dmak]

Steps to reproduce:

• On Windows host, mount some partition (USB drive in my case) to NTFS folder, (say, to C:\shared\usb)
• Create new shared folder, "shared" = "C:\shared".
• Mount the folder in Linux guest.

Result:

• When listing the directory, "usb" is shown as symlink.
• When trying to cd /mnt/shared/usb the following error occurs:

  -bash: cd: /mnt/shared/usb: Protocol error
  

[dmak]

If shared folder is "shared" = "C:\shared\usb", then mount fails:

# mount /mnt/shared
/sbin/mount.vboxsf: mounting failed with the error: Invalid argument

[mlt]

I confirm this issue with 4.3.20 on Windows 8.1 Pro 64 bit. It is enough to symlink a folder (create a junction point) to demonstrate the issue. There is no need in a separate partition. For example, this makes it impossible to start vagrant box from symlinked folder, e.g., one in a convenient location that points somewhere deep into Dropbox tree.