dmesg
    ...
    [    3.833397] systemd[1]: [/usr/lib/systemd/system/dm-event.socket:10]
Unknown lvalue 'RemoveOnStop' in section 'Socket'
    ...


/usr/lib/systemd/system/dm-event.socket
    [Unit]
    Description=Device-mapper event daemon FIFOs
    Documentation=man:dmeventd(8)
    DefaultDependencies=no

    [Socket]
    ListenFIFO=/run/dmeventd-server
    ListenFIFO=/run/dmeventd-client
    SocketMode=0600
    RemoveOnStop=true

    [Install]
    WantedBy=sockets.target

rpm -q --whatprovides /usr/lib/systemd/system/dm-event.socket
    device-mapper-1.02.97-64.1.x86_64


It's mentioed at this RedHat bug

    Bug 1200946 - Unknown lvalue 'RemoveOnStop' in section 'Socket'
(dm-event.socket:10 and vm2-lvmetad.socket:9)
        https://bugzilla.redhat.com/show_bug.cgi?id=1200946#c6

        "OK, systemd-219-1.el7 (or higher) is currently prepared for 7.2. This
version is recent enought to recognize the "RemoveOnStop" option. Marking this
as resolved in current release."

On OpenSUSE it's too old

    systemctl --version
        systemd 210
        +PAM +LIBWRAP +AUDIT +SELINUX -IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT
+ACL +XZ +SECCOMP +APPARMOR

For OpenSUSE Leap 42.1 that 

    RemoveOnStop=true

should probably be replaced with something usable, like a shell script that
execs on unit stop.

Here's another example of OpenSUSE's old systemd failing cuz of newer keywords.

https://bugzilla.opensuse.org/show_bug.cgi?id=954482