ecryptfs-recover-private doesn't fail if invalid key is provided

Invoking `sudo ecryptfs-recover-private /path/to/encrypted/home/` produces

    INFO: Found [/mnt/sdd1/sda5-restore/@home/richter/].
    Try to recover this directory? [Y/n]:
    INFO: Could not find your wrapped passphrase file.
    INFO: To recover this directory, you MUST have your original MOUNT passphrase.
    INFO: When you first setup your encrypted private directory, you were told to record
    INFO: your MOUNT passphrase.
    INFO: It should be 32 characters long, consisting of [0-9] and [a-f].

    Enter your MOUNT passphrase:
    INFO: Success! Private data mounted at [/tmp/ecryptfs.U3NoW30S].

and mounts an empty directory although the password is wrong and `/path/to/encrypted/home/` doesn't point to an `ecryptfs` directory.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: ecryptfs-utils 106-0ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-10.10-generic 3.19.2
Uname: Linux 3.19.0-10-generic x86_64
ApportVersion: 2.16.2-0ubuntu4
Architecture: amd64
CasperVersion: 1.356
CurrentDesktop: Unity
Date: Thu Apr 2 19:03:35 2015
LiveMediaBuild: Ubuntu 15.04 "Vivid Vervet" - Beta amd64 (20150326)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ecryptfs-utils
UpgradeStatus: No upgrade log present (probably fresh install)