Steps to reproduce:
1) Click on a (sub)menu with a lot of items (for me "games" contains some steam stuff, so I used that).
2) Scroll down
3) Move the mouse around items some more, until the whole shell crashes.

Unfortunately I don't have complete debugging/tracing enabled for every library involved, but from the trace it would seem that the problem arises on a remove on a QlistData. My guess is that when I move the mouse down, the "selected item" gets removed. So when i move the mouse around the items, some Hover events happen, but no item gets selected (at least, visually) and then when i stop the mouse it tries to remove void from a "selected" list. This is a guess, as I didn't read the code, and I'm no Qt/C++ expert. 

Here's the relevant part of the trace:

Thread 1 (Thread 0x7fa64f909800 (LWP 2724)):
[KCrash Handler]
#5  0x00007fa6488aff01 in __memmove_ssse3_back () from /usr/lib/libc.so.6
#6  0x00007fa648f37e69 in QListData::remove(int) () from /usr/lib/libQt5Core.so.5
#7  0x00007fa648f38109 in QListData::erase(void**) () from /usr/lib/libQt5Core.so.5
#8  0x00007fa64f399f62 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#9  0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#10 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#11 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#12 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#13 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#14 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#15 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#16 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#17 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#18 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#19 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#20 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#21 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#22 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#23 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#24 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#25 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#26 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#27 0x00007fa64f399b40 in QQuickWindowPrivate::deliverHoverEvent(QQuickItem*, QPointF const&, QPointF const&, QFlags<Qt::KeyboardModifier>, bool&) () from /usr/lib/libQt5Quick.so.5
#28 0x00007fa64f39c0ec in QQuickWindow::mouseMoveEvent(QMouseEvent*) () from /usr/lib/libQt5Quick.so.5
#29 0x00007fa6495ebe45 in QWindow::event(QEvent*) () from /usr/lib/libQt5Gui.so.5
#30 0x00007fa64f39d333 in QQuickWindow::event(QEvent*) () from /usr/lib/libQt5Quick.so.5
#31 0x00007fa64e2b7839 in PlasmaQuick::Dialog::event(QEvent*) () from /usr/lib/libKF5PlasmaQuick.so.5
#32 0x00007fa649d7115c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#33 0x00007fa649d766ee in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#34 0x00007fa6490bcaeb in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#35 0x00007fa6495e4470 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) () from /usr/lib/libQt5Gui.so.5
#36 0x00007fa6495e5cc5 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () from /usr/lib/libQt5Gui.so.5
#37 0x00007fa6495cb42f in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Gui.so.5
#38 0x00007fa63b2245d0 in ?? () from /usr/lib/qt/plugins/platforms/libqxcb.so
#39 0x00007fa643af7b84 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#40 0x00007fa643af7dc8 in ?? () from /usr/lib/libglib-2.0.so.0
#41 0x00007fa643af7e6c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#42 0x00007fa649113ec7 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#43 0x00007fa6490ba512 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#44 0x00007fa6490c1ecc in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#45 0x000000000042eddd in main ()