Comment # 6 on bug 1012883 from Franck Bui

Ok I've been able to reproduce a similar issue on Leap 42.2 with KDE as default
DE (like you).

Apparently when closing the session, the process "ksmserver" was reacting badly
to the TERM signal sent by systemd. The process was stuck somewhere in its
signal handler:

(gdb) bt
#0  0x00007f70e869ef66 in waitpid () from /lib64/libc.so.6
#1  0x00007f70e126fbf2 in ?? () from /usr/lib64/libKF5Crash.so.5
#2  0x00007f70e12706d4 in KCrash::defaultCrashHandler(int) () from
/usr/lib64/libKF5Crash.so.5
#3  <signal handler called>
#4  0x00007f70e59b8883 in ?? () from /usr/lib64/libKF5GlobalAccel.so.5
#5  0x00007f70e59b2bab in ?? () from /usr/lib64/libKF5GlobalAccel.so.5
#6  0x00007f70e2fc01c3 in QMetaObject::activate(QObject*, int, int, void**) ()
    from /usr/lib64/libQt5Core.so.5
#7  0x00007f70e2fc07af in QObject::destroyed(QObject*) () from
/usr/lib64/libQt5Core.so.5
#8  0x00007f70e2fc825e in QObject::~QObject() () from
/usr/lib64/libQt5Core.so.5
#9  0x00007f70e3c93bd8 in QAction::~QAction() () from
/usr/lib64/libQt5Widgets.so.5
#10 0x00007f70e3c93bf9 in QAction::~QAction() () from
/usr/lib64/libQt5Widgets.so.5
#11 0x00007f70e2fbeaa5 in QObjectPrivate::deleteChildren() () from
/usr/lib64/libQt5Core.so.5
#12 0x00007f70e2fc7fbe in QObject::~QObject() () from
/usr/lib64/libQt5Core.so.5
#13 0x00007f70e5c1ffbe in KActionCollection::~KActionCollection() () from
/usr/lib64/libKF5XmlGui.so.5
#14 0x00007f70e5c20069 in KActionCollection::~KActionCollection() () from
/usr/lib64/libKF5XmlGui.so.5
#15 0x00007f70e2fbeaa5 in QObjectPrivate::deleteChildren() () from
/usr/lib64/libQt5Core.so.5
#16 0x00007f70e2fc7fbe in QObject::~QObject() () from
/usr/lib64/libQt5Core.so.5
#17 0x00007f70e89a1389 in KSMServer::~KSMServer (this=0x26b5620,
__in_chrg=<optimized out>)
    at /usr/src/debug/plasma-workspace-5.8.3/ksmserver/server.cpp:733
#18 0x00007f70e899f75c in sighandler (sig=<optimized out>)
    at /usr/src/debug/plasma-workspace-5.8.3/ksmserver/server.cpp:539
#19 <signal handler called>
#20 sighandler (sig=1) at
/usr/src/debug/plasma-workspace-5.8.3/ksmserver/server.cpp:529
#21 <signal handler called>
#22 0x00007f70d6a30bd0 in ?? () from /usr/lib64/libgbm.so.1
#23 0x00007f70e8bdf21a in _dl_fini () from /lib64/ld-linux-x86-64.so.2
#24 0x00007f70e861c139 in __run_exit_handlers () from /lib64/libc.so.6
#25 0x00007f70e861c185 in exit () from /lib64/libc.so.6
#26 0x00007f70d305addd in QXcbConnection::processXcbEvents() () from
/usr/lib64/libQt5XcbQpa.so.5
#27 0x00007f70e2fc1166 in QObject::event(QEvent*) () from
/usr/lib64/libQt5Core.so.5
#28 0x00007f70e3c9ce3c in QApplicationPrivate::notify_helper(QObject*, QEvent*)
()
    from /usr/lib64/libQt5Widgets.so.5
#29 0x00007f70e3ca149a in QApplication::notify(QObject*, QEvent*) () from
/usr/lib64/libQt5Widgets.so.5
#30 0x00007f70e2f95fc5 in QCoreApplication::notifyInternal2(QObject*, QEvent*)
()
    from /usr/lib64/libQt5Core.so.5
#31 0x00007f70e2f97daa in QCoreApplicationPrivate::sendPostedEvents(QObject*,
int, QThreadData*) ()
    from /usr/lib64/libQt5Core.so.5
#32 0x00007f70e2fe6c83 in ?? () from /usr/lib64/libQt5Core.so.5
#33 0x00007f70dcbb6134 in g_main_context_dispatch () from
/usr/lib64/libglib-2.0.so.0
#34 0x00007f70dcbb6388 in ?? () from /usr/lib64/libglib-2.0.so.0
#35 0x00007f70dcbb642c in g_main_context_iteration () from
/usr/lib64/libglib-2.0.so.0
#36 0x00007f70e2fe632b in
QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
    from /usr/lib64/libQt5Core.so.5
#37 0x00007f70e2f93fdb in
QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
    from /usr/lib64/libQt5Core.so.5
#38 0x00007f70e2f9bec6 in QCoreApplication::exec() () from
/usr/lib64/libQt5Core.so.5
#39 0x00007f70e899b4f7 in kdemain (argc=1, argv=<optimized out>)
    at /usr/src/debug/plasma-workspace-5.8.3/ksmserver/main.cpp:349
#40 0x00007f70e86056e5 in __libc_start_main () from /lib64/libc.so.6
#41 0x0000000000400839 in _start () at ../sysdeps/x86_64/start.S:118
(gdb)

KDE team, could you give a look at the backtrace ?