systemd-nspawn --network-interface= disappears when container exits

[Tero Marttila]

On Ubuntu xenial,

 $ lsb_release -rd
 Description: Ubuntu 16.04 LTS
 Release: 16.04
 $ apt-cache policy systemd
 systemd:
   Installed: 229-4ubuntu4
   Candidate: 229-4ubuntu4
   Version table:
  *** 229-4ubuntu4 500
  500 http://apt/ubuntu xenial/main amd64 Packages
  100 /var/lib/dpkg/status

The systemd-nspawn manpage states that the existing --network-interface= device should be returned to the host's namespace on exit:

       --network-interface=
           Assign the specified network interface to the container. This will remove the specified interface from the calling namespace
           and place it in the container. *When the container terminates, it is moved back to the host namespace*. Note that
           --network-interface= implies --private-network. This option may be used more than once to add multiple network interfaces to
           the container.

However, this does not appear to be the case for a VLAN interface (created using systemd-networkd):

 $ ip link
 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
     link/ether 00:26:b9:5a:45:03 brd ff:ff:ff:ff:ff:ff
 3: eno2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ether 00:26:b9:5a:45:04 brd ff:ff:ff:ff:ff:ff
 6: vlan-terom-dev@eno1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ether 66:c9:35:09:49:74 brd ff:ff:ff:ff:ff:ff
 $ sudo systemd-nspawn -M obelix-terom-dev --network-interface=vlan-terom-dev bash
 Spawning container obelix-terom-dev on /var/lib/machines/.#machine.obelix-terom-devfc1e2f39f5df67dd.
 Press ^] three times within 1s to kill container.
 mount(/var/lib/machines/obelix-terom-dev/sys/fs/selinux) failed, ignoring: No such file or directory
 mount(/var/lib/machines/obelix-terom-dev/sys/fs/selinux) failed, ignoring: Invalid argument
 /etc/localtime is not a symlink, not updating container timezone.
 root@obelix-terom-dev:/# ip link
 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 6: vlan-terom-dev@if2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ether 66:c9:35:09:49:74 brd ff:ff:ff:ff:ff:ff link-netnsid 0
 root@obelix-terom-dev:/# exit
 Container obelix-terom-dev exited successfully.
 $ ip link
 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
     link/ether 00:26:b9:5a:45:03 brd ff:ff:ff:ff:ff:ff
 3: eno2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
     link/ether 00:26:b9:5a:45:04 brd ff:ff:ff:ff:ff:ff
 $ sudo systemd-nspawn -M obelix-terom-dev --network-interface=vlan-terom-dev bash
 Spawning container obelix-terom-dev on /var/lib/machines/obelix-terom-dev.
 Press ^] three times within 1s to kill container.
 Failed to resolve interface vlan-terom-dev: No such device
 mount(/var/lib/machines/obelix-terom-dev/sys/fs/selinux) failed, ignoring: No such file or directory
 mount(/var/lib/machines/obelix-terom-dev/sys/fs/selinux) failed, ignoring: Invalid argument
 /etc/localtime is not a symlink, not updating container timezone.
 $

Possibly related upstream mailing list thread, including workarounds:

        https://lists.freedesktop.org/archives/systemd-devel/2015-April/030934.html

Is this just a documentation bug in the man page?