Fails silently to mount on WebDAV filesystem

An ecrpytfs mount fails without any message when I attempt to stack it on a WebDAV filesystem. This problem was also noted at the expired question at https://answers.launchpad.net/ecryptfs/+question/96477

First my fstab entry:
        http://webdav.4shared.com:80/wa /home/tcl/4shared davfs rw,user,no

The attempted mount sequence. All appears good until the ls fails with 'Invalid argument' regarding the encrypted directory.

tcl@gilbereth:~$ mount 4shared/
/sbin/mount.davfs: warning: the server does not support locks
tcl@gilbereth:~$ sudo mount -t ecryptfs ~/4shared/ ~/vvv/
[sudo] password for tcl:
Passphrase:
Select cipher:
 1) aes: blocksize = 16; min keysize = 16; max keysize = 32 (not loaded)
 2) blowfish: blocksize = 16; min keysize = 16; max keysize = 56 (not loaded)
 3) des3_ede: blocksize = 8; min keysize = 24; max keysize = 24 (not loaded)
 4) twofish: blocksize = 16; min keysize = 16; max keysize = 32 (not loaded)
 5) cast6: blocksize = 16; min keysize = 16; max keysize = 32 (not loaded)
 6) cast5: blocksize = 8; min keysize = 5; max keysize = 16 (not loaded)
Selection [aes]:
Select key bytes:
 1) 16
 2) 32
 3) 24
Selection [16]:
Enable plaintext passthrough (y/n) [n]:
Enable filename encryption (y/n) [n]:
Attempting to mount with the following options:
  ecryptfs_unlink_sigs
  ecryptfs_key_bytes=16
  ecryptfs_cipher=aes
  ecryptfs_sig=83000bfe5456fb3d
WARNING: Based on the contents of [/root/.ecryptfs/sig-cache.txt],
 3) 24
Selection [16]:
Enable plaintext passthrough (y/n) [n]:
Enable filename encryption (y/n) [n]:
Attempting to mount with the following options:
  ecryptfs_unlink_sigs
  ecryptfs_key_bytes=16
  ecryptfs_cipher=aes
  ecryptfs_sig=83000bfe5456fb3d
WARNING: Based on the contents of [/root/.ecryptfs/sig-cache.txt],
it looks like you have never mounted with this key
before. This could mean that you have typed your
passphrase wrong.

Would you like to proceed with the mount (yes/no)? : yes
Would you like to append sig [83000bfe5456fb3d] to
[/root/.ecryptfs/sig-cache.txt]
in order to avoid this warning in the future (yes/no)? : no
Not adding sig to user sig cache file; continuing with mount.
Mounted eCryptfs
tcl@gilbereth:~$ cd vvv
tcl@gilbereth:~/vvv$ ls
ls: cannot open directory .: Invalid argument
tcl@gilbereth:~/vvv$ cd ~/4shared/
tcl@gilbereth:~/4shared$ ls
fred lost+found
tcl@gilbereth: