just as the title says. Using today's build 16.11.70.

Reproducible: Always

Steps to Reproduce:
1. open kdenlive
2. try to delete a track


Actual Results:  
it crashes

Expected Results:  
the track should be deleted.

Thread 1 "kdenlive" received signal SIGSEGV, Segmentation fault.
0x00007ffff6fa330c in mlt_service_connect_producer () from /usr/lib/libmlt.so.6
(gdb) backtrace
#0  0x00007ffff6fa330c in mlt_service_connect_producer () from /usr/lib/libmlt.so.6
#1  0x00007ffff6fac4a9 in mlt_transition_connect () from /usr/lib/libmlt.so.6
#2  0x00007ffff6facd07 in mlt_field_plant_transition () from /usr/lib/libmlt.so.6
#3  0x00000000005d9e80 in ?? ()
#4  0x00000000005bb502 in ?? ()
#5  0x00000000005828c0 in ?? ()
#6  0x00007ffff1df21be in QUndoCommand::redo() () from /usr/lib/libQt5Widgets.so.5
#7  0x00007ffff1df4198 in QUndoStack::push(QUndoCommand*) () from /usr/lib/libQt5Widgets.so.5
#8  0x00000000005792c5 in ?? ()
#9  0x0000000000579df0 in ?? ()
#10 0x000000000083ed6d in ?? ()
#11 0x00007ffff0a6685e in QMetaObject::activate(QObject*, int, int, void**) ()
   from /usr/lib/libQt5Core.so.5
#12 0x00007ffff1a7d472 in QAction::triggered(bool) () from /usr/lib/libQt5Widgets.so.5
#13 0x00007ffff1a7fe60 in QAction::activate(QAction::ActionEvent) () from /usr/lib/libQt5Widgets.so.5
#14 0x00007ffff1bedeea in ?? () from /usr/lib/libQt5Widgets.so.5
#15 0x00007ffff1bf40ec in ?? () from /usr/lib/libQt5Widgets.so.5
#16 0x00007ffff1bf80e0 in QMenu::mouseReleaseEvent(QMouseEvent*) () from /usr/lib/libQt5Widgets.so.5
#17 0x00007ffff1acaf18 in QWidget::event(QEvent*) () from /usr/lib/libQt5Widgets.so.5
#18 0x00007ffff1bf8b9b in QMenu::event(QEvent*) () from /usr/lib/libQt5Widgets.so.5
#19 0x00007ffff1a83e3c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#20 0x00007ffff1a8c46d in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#21 0x00007ffff0a3ac80 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
---Type <return> to continue, or q <return> to quit---
#22 0x00007ffff1a8ab1d in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) () from /usr/lib/libQt5Widgets.so.5
#23 0x00007ffff1ae55a0 in ?? () from /usr/lib/libQt5Widgets.so.5
#24 0x00007ffff1ae7763 in ?? () from /usr/lib/libQt5Widgets.so.5
#25 0x00007ffff1a83e3c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#26 0x00007ffff1a8b5b1 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#27 0x00007ffff0a3ac80 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#28 0x00007ffff0f890e3 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) () from /usr/lib/libQt5Gui.so.5
#29 0x00007ffff0f8ac65 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () from /usr/lib/libQt5Gui.so.5
#30 0x00007ffff0f68cbb in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Gui.so.5
#31 0x00007fffdd921310 in ?? () from /usr/lib/libQt5XcbQpa.so.5
#32 0x00007fffe809add7 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#33 0x00007fffe809b040 in ?? () from /usr/lib/libglib-2.0.so.0
#34 0x00007fffe809b0ec in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#35 0x00007ffff0a8f57f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib/libQt5Core.so.5
#36 0x00007ffff0a390da in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib/libQt5Core.so.5
#37 0x00007ffff1bf303d in QMenu::exec(QPoint const&, QAction*) () from /usr/lib/libQt5Widgets.so.5
#38 0x00007ffff1bf31e0 in QMenu::exec(QList<QAction*>, QPoint const&, QAction*, QWidget*) ()
---Type <return> to continue, or q <return> to quit---
   from /usr/lib/libQt5Widgets.so.5
#39 0x00007ffff1acbbba in QWidget::event(QEvent*) () from /usr/lib/libQt5Widgets.so.5
#40 0x00007ffff1a83e3c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#41 0x00007ffff1a8c6f0 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#42 0x00007ffff0a3ac80 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#43 0x00007ffff1ae5111 in ?? () from /usr/lib/libQt5Widgets.so.5
#44 0x00007ffff1ae7763 in ?? () from /usr/lib/libQt5Widgets.so.5
#45 0x00007ffff1a83e3c in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQt5Widgets.so.5
#46 0x00007ffff1a8b5b1 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#47 0x00007ffff0a3ac80 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib/libQt5Core.so.5
#48 0x00007ffff0f890e3 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) () from /usr/lib/libQt5Gui.so.5
#49 0x00007ffff0f8ac65 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () from /usr/lib/libQt5Gui.so.5
#50 0x00007ffff0f68cbb in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Gui.so.5
#51 0x00007fffdd921310 in ?? () from /usr/lib/libQt5XcbQpa.so.5
#52 0x00007fffe809add7 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#53 0x00007fffe809b040 in ?? () from /usr/lib/libglib-2.0.so.0
#54 0x00007fffe809b0ec in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#55 0x00007ffff0a8f57f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
---Type <return> to continue, or q <return> to quit---
   from /usr/lib/libQt5Core.so.5
#56 0x00007ffff0a390da in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib/libQt5Core.so.5
#57 0x00007ffff0a415cc in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#58 0x000000000048aa22 in ?? ()
#59 0x00007fffefda8741 in __libc_start_main () from /usr/lib/libc.so.6
#60 0x000000000048b2e9 in _start ()