This was actually a one time crash, that I can't reproduce anymore.
Plasmashell crashed a moment before, there is a separate bug report for that: 
https://bugs.kde.org/show_bug.cgi?id=396100

Steps to Reproduce:

1) Drag a file
2) Move it over Task Manager
3) Move it out of the Task Manager

Actual Results:
kwin crashes

Expected Results:
kwin does not crash

Additional Information:
openSuSE Tumbleweed 20180629
Qt 5.11.1
KF 5.47.0
plasma 5.13.1
Linux 4.17.3-1-default 64-bit
Wayland

Stack trace:
#0  0x00007ff09d46fd03 in KWayland::Server::DataDeviceInterface::updateDragTarget(KWayland::Server::SurfaceInterface*, unsigned int) (this=0x55d9a6f6e4f0, surface=surface@entry=0x0, serial=serial@entry=5643)
    at /usr/src/debug/kwayland-5.47.0-1.2.x86_64/src/server/datadevice_interface.cpp:256
#1  0x00007ff09d48fa70 in KWayland::Server::SeatInterface::setDragTarget(KWayland::Server::SurfaceInterface*, QPointF const&, QMatrix4x4 const&) (this=0x55d9a6818340, surface=0x55d9a755a690, globalPosition=..., inputTransformation=...) at /usr/src/debug/kwayland-5.47.0-1.2.x86_64/src/server/seat_interface.cpp:649
#2  0x00007ff09e51a52d in KWin::DragAndDropInputFilter::pointerEvent(QMouseEvent*, unsigned int) (this=<optimized out>, event=0x7fff3285e540, nativeButton=<optimized out>) at /usr/src/debug/kwin5-5.13.1-1.1.x86_64/toplevel.h:824
#3  0x00007ff09e52cb78 in std::__invoke_impl<bool, bool (KWin::InputEventFilter::*&)(QMouseEvent*, unsigned int), KWin::InputEventFilter* const&, KWin::MouseEvent*&, int&>(std::__invoke_memfun_deref, bool (KWin::InputEventFilter::*&)(QMouseEvent*, unsigned int), KWin::InputEventFilter* const&, KWin::MouseEvent*&, int&) (__f=@0x7fff3285e4e0: &virtual table offset 16, __f=@0x7fff3285e4e0: &virtual table offset 16, __t=@0x55d9a6818758: 0x55d9a6d0f0d0)
    at /usr/include/c++/8/bits/invoke.h:89
#4  0x00007ff09e52cb78 in std::__invoke<bool (KWin::InputEventFilter::*&)(QMouseEvent*, unsigned int), KWin::InputEventFilter* const&, KWin::MouseEvent*&, int&>(bool (KWin::InputEventFilter::*&)(QMouseEvent*, unsigned int), KWin::InputEventFilter* const&, KWin::MouseEvent*&, int&) (__fn=@0x7fff3285e4e0: &virtual table offset 16) at /usr/include/c++/8/bits/invoke.h:95
#5  0x00007ff09e52cb78 in std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)>::__call<bool, KWin::InputEventFilter* const&, 0ul, 1ul, 2ul>(std::tuple<KWin::InputEventFilter* const&>&&, std::_Index_tuple<0ul, 1ul, 2ul>) (__args=..., this=0x7fff3285e4e0) at /usr/include/c++/8/functional:400
#6  0x00007ff09e52cb78 in std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)>::operator()<KWin::InputEventFilter* const&, bool>(KWin::InputEventFilter* const&) (this=0x7fff3285e4e0) at /usr/include/c++/8/functional:484
#7  0x00007ff09e52cb78 in __gnu_cxx::__ops::_Iter_pred<std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >::operator()<KWin::InputEventFilter* const*>(KWin::InputEventFilter* const*) (__it=0x55d9a6818758, this=0x7fff3285e4e0) at /usr/include/c++/8/bits/predefined_ops.h:283
#8  0x00007ff09e52cb78 in std::__find_if<KWin::InputEventFilter* const*, __gnu_cxx::__ops::_Iter_pred<std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> > >(KWin::InputEventFilter* const*, KWin::InputEventFilter* const*, __gnu_cxx::__ops::_Iter_pred<std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >, std::random_access_iterator_tag) (__first=0x55d9a6818758, __last=0x55d9a68187c8, __pred=...) at /usr/include/c++/8/bits/stl_algo.h:128
#9  0x00007ff09e528407 in std::__find_if<KWin::InputEventFilter* const*, __gnu_cxx::__ops::_Iter_pred<std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> > >(KWin::InputEventFilter* const*, KWin::InputEventFilter* const*, __gnu_cxx::__ops::_Iter_pred<std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >) (__pred=..., __last=<optimized out>, __first=<optimized out>) at /usr/include/c++/8/bits/stl_algo.h:159
#10 0x00007ff09e528407 in std::find_if<KWin::InputEventFilter* const*, std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >(KWin::InputEventFilter* const*, KWin::InputEventFilter* const*, std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)>) (__pred=..., __last=<optimized out>, __first=<optimized out>)
    at /usr/include/c++/8/bits/stl_algo.h:3930
#11 0x00007ff09e528407 in std::none_of<KWin::InputEventFilter* const*, std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >(KWin::InputEventFilter* const*, KWin::InputEventFilter* const*, std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)>) (__pred=..., __last=<optimized out>, __first=<optimized out>)
    at /usr/include/c++/8/bits/stl_algo.h:526
#12 0x00007ff09e528407 in std::any_of<KWin::InputEventFilter* const*, std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >(KWin::InputEventFilter* const*, KWin::InputEventFilter* const*, std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)>) (__pred=..., __last=<optimized out>, __first=<optimized out>)
    at /usr/include/c++/8/bits/stl_algo.h:544
#13 0x00007ff09e528407 in KWin::InputRedirection::processFilters<std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)> >(std::_Bind<bool (KWin::InputEventFilter::*(std::_Placeholder<1>, KWin::MouseEvent*, int))(QMouseEvent*, unsigned int)>) (function=..., this=<optimized out>) at /usr/src/debug/kwin5-5.13.1-1.1.x86_64/input.h:189
#14 0x00007ff09e528407 in KWin::PointerInputRedirection::processMotion(QPointF const&, QSizeF const&, QSizeF const&, unsigned int, unsigned long long, KWin::LibInput::Device*) (this=0x55d9a6816080, pos=..., delta=..., deltaNonAccelerated=..., time=2625875, timeUsec=2625875075, device=0x55d9a6935a20) at /usr/src/debug/kwin5-5.13.1-1.1.x86_64/pointer_input.cpp:305
#15 0x00007ff09e511cd5 in KWin::InputRedirection::<lambda(const QSizeF&, const QSizeF&, uint32_t, quint64, KWin::LibInput::Device*)>::operator() (__closure=<optimized out>, device=<optimized out>, timeMicroseconds=<optimized out>, time=<optimized out>, deltaNonAccel=..., delta=...) at /usr/include/qt5/QtCore/qpoint.h:287
#16 0x00007ff09e511cd5 in QtPrivate::FunctorCall<QtPrivate::IndexesList<0, 1, 2, 3, 4>, QtPrivate::List<const QSizeF&, const QSizeF&, unsigned int, long long unsigned int, KWin::LibInput::Device*>, void, KWin::InputRedirection::setupLibInput()::<lambda(const QSizeF&, const QSizeF&, uint32_t, quint64, KWin::LibInput::Device*)> >::call (arg=<optimized out>, f=...) at /usr/include/qt5/QtCore/qobjectdefs_impl.h:128
#17 0x00007ff09e511cd5 in QtPrivate::Functor<KWin::InputRedirection::setupLibInput()::<lambda(const QSizeF&, const QSizeF&, uint32_t, quint64, KWin::LibInput::Device*)>, 5>::call<QtPrivate::List<QSizeF const&, QSizeF const&, unsigned int, unsigned long long, KWin::LibInput::Device*>, void> (arg=<optimized out>, f=...) at /usr/include/qt5/QtCore/qobjectdefs_impl.h:238
#18 0x00007ff09e511cd5 in QtPrivate::QFunctorSlotObject<KWin::InputRedirection::setupLibInput()::<lambda(const QSizeF&, const QSizeF&, uint32_t, quint64, KWin::LibInput::Device*)>, 5, QtPrivate::List<const QSizeF&, const QSizeF&, unsigned int, long long unsigned int, KWin::LibInput::Device*>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void **, bool *) (which=<optimized out>, this_=<optimized out>, r=<optimized out>, a=<optimized out>, ret=<optimized out>) at /usr/include/qt5/QtCore/qobjectdefs_impl.h:421
#19 0x00007ff09c05fd70 in QMetaObject::activate(QObject*, int, int, void**) () at /usr/lib64/libQt5Core.so.5
#20 0x00007ff09e666b89 in KWin::LibInput::Connection::pointerMotion(QSizeF const&, QSizeF const&, unsigned int, unsigned long long, KWin::LibInput::Device*) (this=this@entry=0x55d9a6925740, _t1=..., _t2=..., _t3=<optimized out>, _t3@entry=2625875, _t4=<optimized out>, _t4@entry=2625875075, _t5=<optimized out>) at /usr/src/debug/kwin5-5.13.1-1.1.x86_64/build/kwin_autogen/PCJB6APXE6/moc_connection.cpp:549
#21 0x00007ff09e637733 in KWin::LibInput::Connection::processEvents() (this=0x55d9a6925740) at /usr/src/debug/kwin5-5.13.1-1.1.x86_64/libinput/connection.cpp:398
#22 0x00007ff09c060482 in QObject::event(QEvent*) () at /usr/lib64/libQt5Core.so.5
#23 0x00007ff09c638c11 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib64/libQt5Widgets.so.5
#24 0x00007ff09c63fdf0 in QApplication::notify(QObject*, QEvent*) () at /usr/lib64/libQt5Widgets.so.5
#25 0x00007ff09c037da9 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib64/libQt5Core.so.5
#26 0x00007ff09c03ac6b in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () at /usr/lib64/libQt5Core.so.5
#27 0x00007ff09c08409b in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib64/libQt5Core.so.5
#28 0x00007ff08675218d in QUnixEventDispatcherQPA::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=<optimized out>, flags=...) at qunixeventdispatcher.cpp:68
#29 0x00007ff09c036bbb in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib64/libQt5Core.so.5
#30 0x00007ff09c03e94e in QCoreApplication::exec() () at /usr/lib64/libQt5Core.so.5
#31 0x000055d9a5a08bc3 in main(int, char**) (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/kwin5-5.13.1-1.1.x86_64/main_wayland.cpp:924