Logout umounts encrypted home only every second logout (console|ssh)

* I've created a user with adduser --encrypted-home testuser.
* when I login via console and logout afterwards with ctrl + d the encrypted Filesystem is still mounted.
* if I login again and logout via ctrl + d the encrypted filesystem is succesfully dismounted.
* with ssh there is the same behavior but: After logout the first time there is a remaining ssh process of the testuser. I have to kill this process to reproduce the effect. If I don't kill that Process the mount will stay for ever.
* This remaining ssh process belongs to the init process:
pstree -s 10680
systemd───sshd

The apport report:

ProblemType: Bug
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
Date: Thu Jun 23 11:15:25 2016
Dependencies:
 adduser 3.113+nmu3ubuntu4
 apt 1.2.12~ubuntu16.04.1
 apt-utils 1.2.12~ubuntu16.04.1
 base-files 9.4ubuntu4
 busybox-initramfs 1:1.22.0-15ubuntu1
 busybox-static 1:1.22.0-15ubuntu1
 console-setup 1.108ubuntu15
 console-setup-linux 1.108ubuntu15
 coreutils 8.25-2ubuntu2
 cpio 2.11+dfsg-5ubuntu1
 cryptsetup 2:1.6.6-5ubuntu2
 cryptsetup-bin 2:1.6.6-5ubuntu2
 debconf 1.5.58ubuntu1
 debconf-i18n 1.5.58ubuntu1
 debianutils 4.7
 distro-info-data 0.28ubuntu0.1
 dmsetup 2:1.02.110-1ubuntu10
 dpkg 1.18.4ubuntu1.1
 e2fslibs 1.42.13-1ubuntu1
 e2fsprogs 1.42.13-1ubuntu1
 gcc-5-base 5.3.1-14ubuntu2.1
 gcc-6-base 6.0.1-0ubuntu1
 gettext-base 0.19.7-2ubuntu3
 gnupg 1.4.20-1ubuntu3
 gpgv 1.4.20-1ubuntu3
 init-system-helpers 1.29ubuntu2
 initramfs-tools 0.122ubuntu8.1
 initramfs-tools-bin 0.122ubuntu8.1
 initramfs-tools-core 0.122ubuntu8.1
 initscripts 2.88dsf-59.3ubuntu2
 insserv 1.14.0-5ubuntu3
 kbd 1.15.5-1ubuntu4
 keyboard-configuration 1.108ubuntu15
 keyutils 1.5.9-8ubuntu1
 klibc-utils 2.0.4-8ubuntu1
 kmod 22-1ubuntu4
 libacl1 2.2.52-3
 libapt-inst2.0 1.2.12~ubuntu16.04.1
 libapt-pkg5.0 1.2.12~ubuntu16.04.1
 libasprintf0v5 0.19.7-2ubuntu3
 libattr1 1:2.4.47-2
 libaudit-common 1:2.4.5-1ubuntu2
 libaudit1 1:2.4.5-1ubuntu2
 libblkid1 2.27.1-6ubuntu3.1
 libbz2-1.0 1.0.6-8
 libc6 2.23-0ubuntu3
 libcomerr2 1.42.13-1ubuntu1
 libcryptsetup4 2:1.6.6-5ubuntu2
 libdb5.3 5.3.28-11
 libdevmapper1.02.1 2:1.02.110-1ubuntu10
 libdrm2 2.4.67-1ubuntu0.16.04.1
 libecryptfs1 111-0ubuntu1
 libfdisk1 2.27.1-6ubuntu3.1
 libgcc1 1:6.0.1-0ubuntu1
 libgcrypt20 1.6.5-2
 libgpg-error0 1.21-2ubuntu1
 libgpm2 1.20.4-6.1
 libkeyutils1 1.5.9-8ubuntu1
 libklibc 2.0.4-8ubuntu1
 libkmod2 22-1ubuntu4
 liblocale-gettext-perl 1.07-1build1
 liblz4-1 0.0~r131-2ubuntu2
 liblzma5 5.1.1alpha+20120614-2ubuntu2
 libmount1 2.27.1-6ubuntu3.1
 libncurses5 6.0+20160213-1ubuntu1
 libncursesw5 6.0+20160213-1ubuntu1
 libnspr4 2:4.11-1ubuntu1
 libnss3 2:3.21-1ubuntu4
 libnss3-1d 2:3.21-1ubuntu4
 libnss3-nssdb 2:3.21-1ubuntu4
 libpam-modules 1.1.8-3.2ubuntu2
 libpam-modules-bin 1.1.8-3.2ubuntu2
 libpam-runtime 1.1.8-3.2ubuntu2
 libpam0g 1.1.8-3.2ubuntu2
 libpcre3 2:8.38-3.1
 libplymouth4 0.9.2-3ubuntu13.1
 libpng12-0 1.2.54-1ubuntu1
 libpopt0 1.16-10
 libprocps4 2:3.3.10-4ubuntu2
 libreadline6 6.3-8ubuntu2
 libselinux1 2.4-3build2
 libsemanage-common 2.3-1build3
 libsemanage1 2.3-1build3
 libsepol1 2.4-2
 libsmartcols1 2.27.1-6ubuntu3.1
 libsqlite3-0 3.11.0-1ubuntu1
 libss2 1.42.13-1ubuntu1
 libstdc++6 5.3.1-14ubuntu2.1
 libsystemd0 229-4ubuntu6
 libtext-charwidth-perl 0.04-7build5
 libtext-iconv-perl 1.7-5build4
 libtext-wrapi18n-perl 0.06-7.1
 libtinfo5 6.0+20160213-1ubuntu1
 libudev1 229-4ubuntu6
 libusb-0.1-4 2:0.1.12-28
 libustr-1.0-1 1.0.4-5
 libuuid1 2.27.1-6ubuntu3.1
 linux-base 4.0ubuntu1
 lsb-base 9.20160110
 lsb-release 9.20160110
 lsof 4.89+dfsg-0.1
 mount 2.27.1-6ubuntu3.1
 multiarch-support 2.23-0ubuntu3
 passwd 1:4.2-3.1ubuntu5
 perl-base 5.22.1-9
 plymouth 0.9.2-3ubuntu13.1
 plymouth-theme-ubuntu-text 0.9.2-3ubuntu13.1
 procps 2:3.3.10-4ubuntu2
 psmisc 22.21-2.1build1
 readline-common 6.3-8ubuntu2
 rsync 3.1.1-3ubuntu1
 sensible-utils 0.0.9
 sysv-rc 2.88dsf-59.3ubuntu2
 sysvinit-utils 2.88dsf-59.3ubuntu2
 tar 1.28-2.1
 ubuntu-keyring 2012.05.19
 udev 229-4ubuntu6
 util-linux 2.27.1-6ubuntu3.1
 uuid-runtime 2.27.1-6ubuntu3.1
 xkb-data 2.16-1ubuntu1
 zlib1g 1:1.2.8.dfsg-2ubuntu4
DistroRelease: Ubuntu 16.04
InstallationDate: Installed on 2016-06-15 (7 days ago)
InstallationMedia: Ubuntu-Server 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.3)
JournalErrors:
 -- Logs begin at Wed 2016-06-22 18:06:51 CEST, end at Thu 2016-06-23 11:09:04 CEST. --
 Jun 22 18:06:51 hostname kernel: ACPI: RSDP 0x00000000000F6AC0 000024 (v02 PTLTD )
 Jun 22 18:06:51 hostname kernel: ACPI: XSDT 0x00000000BFEE060D 00005C (v01 INTEL 440BX 06040000 VMW 01324272)
 Jun 22 18:06:51 hostname kernel: ACPI: FACP 0x00000000BFEFEE73 0000F4 (v04 INTEL 440BX 06040000 PTL 000F4240)
 Jun 22 18:06:51 hostname kernel: ACPI: DSDT 0x00000000BFEE1175 01DCFE (v01 PTLTD Custom 06040000 MSFT 03000001)
 Jun 22 18:06:51 hostname kernel: ACPI: FACS 0x00000000BFEFFFC0 000040
 Jun 22 18:06:51 hostname kernel: ACPI: FACS 0x00000000BFEFFFC0 000040
 Jun 22 18:06:51 hostname kernel: ACPI: BOOT 0x00000000BFEE114D 000028 (v01 PTLTD $SBFTBL$ 06040000 LTP 00000001)
 Jun 22 18:06:51 hostname kernel: ACPI: APIC 0x00000000BFEE0C3D 0003C2 (v01 PTLTD ? APIC 06040000 LTP 00000000)
 Jun 22 18:06:51 hostname kernel: ACPI: MCFG 0x00000000BFEE0C01 00003C (v01 PTLTD $PCITBL$ 06040000 LTP 00000001)
 Jun 22 18:06:51 hostname kernel: ACPI: SRAT 0x00000000BFEE0709 0004F8 (v02 VMWARE MEMPLUG 06040000 VMW 00000001)
 Jun 22 18:06:51 hostname kernel: ACPI: HPET 0x00000000BFEE06D1 000038 (v01 VMWARE VMW HPET 06040000 VMW 00000001)
 Jun 22 18:06:51 hostname kernel: ACPI: WAET 0x00000000BFEE06A9 000028 (v01 VMWARE VMW WAET 06040000 VMW 00000001)
 Jun 22 18:06:51 hostname kernel: ACPI: 1 ACPI AML tables successfully acquired and loaded
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'cpu cycles' unavailable
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'instructions' unavailable
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'bus cycles' unavailable
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'cache references' unavailable
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'cache misses' unavailable
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'branch instructions' unavailable
 Jun 22 18:06:51 hostname kernel: core: CPUID marked event: 'branch misses' unavailable
 Jun 22 18:06:51 hostname kernel: NMI watchdog: disabled (cpu0): hardware events not enabled
 Jun 22 18:06:51 hostname kernel: PCCT header not found.
 Jun 22 18:06:51 hostname kernel: ACPI Exception: AE_NOT_FOUND, While evaluating Sleep State [\_S2_] (20150930/hwxface-580)
 Jun 22 18:06:51 hostname kernel: ACPI Exception: AE_NOT_FOUND, While evaluating Sleep State [\_S3_] (20150930/hwxface-580)
 Jun 22 18:06:51 hostname kernel: ACPI: Enabled 2 GPEs in block 00 to 0F
 Jun 22 18:06:51 hostname kernel: sd 2:0:0:0: [sda] Assuming drive cache: write through
 Jun 22 18:06:51 hostname kernel: blk_update_request: I/O error, dev fd0, sector 0
 Jun 22 18:06:52 hostname kernel: piix4_smbus 0000:00:07.3: SMBus Host Controller not enabled!
 Jun 22 18:06:53 hostname systemd-udevd[535]: Process '/bin/sh -c 'echo 180 >/sys$DEVPATH/device/timeout'' failed with exit code 2.
 Jun 22 18:06:53 hostname systemd-udevd[533]: Process '/bin/sh -c 'echo 180 >/sys$DEVPATH/device/timeout'' failed with exit code 2.
 Jun 22 18:06:53 hostname systemd-udevd[533]: Process '/bin/sh -c 'echo 180 >/sys$DEVPATH/device/timeout'' failed with exit code 2.
 Jun 22 18:06:53 hostname systemd-udevd[534]: Process '/bin/sh -c 'echo 180 >/sys$DEVPATH/device/timeout'' failed with exit code 2.
 Jun 22 18:06:53 hostname systemd-tmpfiles[767]: [/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log", ignoring.
 Jun 22 18:06:53 hostname systemd-udevd[754]: Process '/bin/sh -c 'echo 180 >/sys$DEVPATH/device/timeout'' failed with exit code 2.
 Jun 22 18:06:54 hostname kernel: cgroup: new mount options do not match the existing superblock, will be ignored
 Jun 22 18:06:55 hostname iscsid[1026]: iSCSI logger with pid=1031 started!
 Jun 22 18:06:55 hostname systemd[1]: Failed to start LXD - container startup/shutdown.
 Jun 22 18:06:55 hostname systemd[1]: lxd-containers.service: Failed with result 'exit-code'.
 Jun 22 18:06:56 hostname iscsid[1031]: iSCSI daemon with pid=1032 started!
 Jun 22 18:10:00 hostname passwd[1411]: pam_ecryptfs: PAM passphrase change module retrieved a NULL passphrase; nothing to do
 Jun 22 18:10:08 hostname passwd[1411]: pam_ecryptfs: PAM passphrase change module retrieved at least one NULL passphrase; nothing to do
 Jun 22 18:22:30 hostname systemd-tmpfiles[1523]: [/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log", ignoring.
 Jun 22 19:35:31 hostname systemd[1]: Failed to start Automatically refresh installed snaps.
 Jun 22 19:35:31 hostname systemd[1]: snapd.refresh.service: Failed with result 'exit-code'.
 Jun 23 00:40:30 hostname systemd[1]: Failed to start Automatically refresh installed snaps.
 Jun 23 00:40:30 hostname systemd[1]: snapd.refresh.service: Failed with result 'exit-code'.
 Jun 23 09:39:30 hostname systemd[1]: Failed to start Automatically refresh installed snaps.
 Jun 23 09:39:30 hostname systemd[1]: snapd.refresh.service: Failed with result 'exit-code'.
 Jun 23 10:14:09 hostname umount.ecryptfs[2226]: Failed to find key with sig [184a87d7f44f5f83]: Required key not available
 Jun 23 10:14:09 hostname umount.ecryptfs[2226]: Failed to find key with sig [7db36707fdf0450d]: Required key not available
 Jun 23 10:20:36 hostname umount.ecryptfs[2343]: Failed to find key with sig [184a87d7f44f5f83]: Required key not available
 Jun 23 10:20:36 hostname umount.ecryptfs[2343]: Failed to find key with sig [7db36707fdf0450d]: Required key not available
Package: ecryptfs-utils 111-0ubuntu1
PackageArchitecture: amd64
ProcEnviron:
 SHELL=/bin/bash
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 LANGUAGE=en_US:en
ProcVersionSignature: Ubuntu 4.4.0-24.43-generic 4.4.10
SourcePackage: ecryptfs-utils
Tags: xenial
Uname: Linux 4.4.0-24-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
_MarkForUpload: True