Mount a subdirectory from an already mounted drive with fstab

I have mounted an external NTFS HD at startup and want to bind a subdirectory to my ~/Documents folder. For this, I added the entries below to fstab, based on this answer:

# Local HD MountsUUID=XXXXXXXXXX   /mnt/dpvs     auto    nosuid,nodev,nofail,x-gvfs-show 0       0# Local binds/mnt/dpvs/Documents     /home/username/Documents   none    defaults,bind   0       0

I can mount the external HD (first entry), but the second entry doesn't work at startup. The directory is empty, Devices shows a "Documents" mount, and unmounting gives me an error (umount: /home/username/Documents: umount failed: Operation not permitted). Strangely, if I boot without the binding entry, then add it to fstab and remount with mount -a, it works.

What can I do to mount this subdirectory?