This crashes

#0  0x000072aeb0ea164c in ?? () from /usr/lib/libc.so.6
#1  0x000072aeb0e51958 in raise () from /usr/lib/libc.so.6
#2  0x000072aeb4896af5 in KCrash::defaultCrashHandler (sig=6)
    at /home/eric/kde/src/kcrash/src/kcrash.cpp:633
#3  <signal handler called>
#4  0x000072aeb0ea164c in ?? () from /usr/lib/libc.so.6
#5  0x000072aeb0e51958 in raise () from /usr/lib/libc.so.6
#6  0x000072aeb0e3b53d in abort () from /usr/lib/libc.so.6
#7  0x000072aeb149fede in QMessageLogger::fatal(char const*, ...) const ()
   from /usr/lib/libQt5Core.so.5
#8  0x000072aeb149ff3c in qt_assert(char const*, char const*, int) ()
   from /usr/lib/libQt5Core.so.5
#9  0x000072aeb4711143 in KateViewManager::moveViewToViewSpace (this=0x5a64bb2e64c0, 
    dest=0x5a64baf74ec0, src=0x5a64bb2e7460, docOrWidget=...)
    at /home/eric/kde/src/kate/apps/lib/kateviewmanager.cpp:1009
#10 0x000072aeb471f305 in KateViewSpace::dropEvent (this=0x5a64baf74ec0, e=0x7ffdfa31e750)
    at /home/eric/kde/src/kate/apps/lib/kateviewspace.cpp:602
#11 0x000072aeb23af558 in QWidget::event(QEvent*) () from /usr/lib/libQt5Widgets.so.5
#12 0x000072aeb2378b1c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#13 0x000072aeb237f016 in QApplication::notify(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#14 0x000072aeb168cf98 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#15 0x000072aeb23cfa94 in ?? () from /usr/lib/libQt5Widgets.so.5
#16 0x000072aeb2378b1c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#17 0x000072aeb168cf98 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#18 0x000072aeb1b49f2f in QGuiApplicationPrivate::processDrop(QWindow*, QMimeData const*, QPoint const&, QFlags<Qt::DropAction>, QFlags<Qt::MouseButton>, QFlags<Qt::KeyboardModifier>) ()
   from /usr/lib/libQt5Gui.so.5
#19 0x000072aeb1b281f6 in QWindowSystemInterface::handleDrop(QWindow*, QMimeData const*, QPoint const&, QFlags<Qt::DropAction>, QFlags<Qt::MouseButton>, QFlags<Qt::KeyboardModifier>) ()
   from /usr/lib/libQt5Gui.so.5
#20 0x000072aeaf8ab5fb in ?? () from /usr/lib/libQt5WaylandClient.so.5
#21 0x000072aeaf0a94f6 in ?? () from /usr/lib/libffi.so.8
#22 0x000072aeaf0a5f5e in ?? () from /usr/lib/libffi.so.8
#23 0x000072aeaf0a8b73 in ffi_call () from /usr/lib/libffi.so.8
#24 0x000072aeb0e0e645 in ?? () from /usr/lib/libwayland-client.so.0
#25 0x000072aeb0e0ee03 in ?? () from /usr/lib/libwayland-client.so.0
#26 0x000072aeb0e0effc in wl_display_dispatch_

I tried dragging a widget tab between viewspaces

@eric yeah, the assert was wrong. fixed in master