#0  0x00007ffff493449b in raise () at /usr/lib/x86_64-linux-gnu/libc.so.6
#1  0x00007ffff491d857 in abort () at /usr/lib/x86_64-linux-gnu/libc.so.6
#2  0x00007ffff4978bd7 in __libc_message ()
    at /usr/lib/x86_64-linux-gnu/libc.so.6
#3  0x00007ffff4980bea in  () at /usr/lib/x86_64-linux-gnu/libc.so.6
#4  0x00007ffff4981e9c in _int_free () at /usr/lib/x86_64-linux-gnu/libc.so.6
#5  0x00007ffff4985e63 in free () at /usr/lib/x86_64-linux-gnu/libc.so.6
#6  0x00007ffff7b0e7e2 in __gnu_cxx::new_allocator<std::_List_node<unsigned int> >::deallocate(std::_List_node<unsigned int>*, unsigned long)
    (__t=1, __p=0x5555582a9458, this=0x5555582a9458)
    at /usr/include/c++/11.3.0/ext/new_allocator.h:132
#7  std::allocator_traits<std::allocator<std::_List_node<unsigned int> > >::deallocate(std::allocator<std::_List_node<unsigned int> >&, std::_List_node<unsigned int>*, unsigned long) (__n=1, __p=0x5555582a9458, __a=...)
    at /usr/include/c++/11.3.0/bits/alloc_traits.h:496
#8  std::__cxx11::_List_base<unsigned int, std::allocator<unsigned int> >::_M_put_node(std::_List_node<unsigned int>*)
    (__p=0x5555582a9458, this=0x5555582a9458)
    at /usr/include/c++/11.3.0/bits/stl_list.h:446
#9  std::__cxx11::list<unsigned int, std::allocator<unsigned int> >::_M_erase(std::_List_iterator<unsigned int>)Python Exception <class 'gdb.error'>: value has been optimized out
 (__position=, this=0x5555582a9458)
    at /usr/include/c++/11.3.0/bits/stl_list.h:1930
#10 std::__cxx11::list<unsigned int, std::allocator<unsigned int> >::pop_front()
 (this=0x5555582a9458) at /usr/include/c++/11.3.0/bits/stl_list.h:1198
#11 ARDOUR::Session::commit_reversible_command(Command*) (this=0x5555582a7000, cmd=<optimized out>) at ../libs/ardour/session_state.cc:3179
#12 0x0000555555cb4176 in Drag::end_grab(_GdkEvent*) (this=0x555558fe8f00, event=0x7fffffffd0f0) at ../gtk2_ardour/editor_drag.cc:354
#13 0x0000555555cb68ab in DragManager::end_grab(_GdkEvent*) (this=0x555557b50d00, e=e@entry=0x7fffffffd0f0) at ../gtk2_ardour/editor_drag.cc:185
#14 0x0000555555fbaa37 in MidiRegionView::button_release(_GdkEventButton*) (this=0x5555584ace60, ev=0x7fffffffd0f0) at ../gtk2_ardour/midi_region_view.cc:594
#15 0x00007ffff6f6f5e7 in sigc::internal::signal_emit1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >::operator()(sigc::slot<bool, _GdkEvent*, sigc::nil, sigc::nil, sigc::nil, sigc::nil, sigc::nil, sigc::nil> const&) const (_A_slot=..., this=<synthetic pointer>) at /app/include/sigc++-2.0/sigc++/signal.h:829
#16 sigc::internal::slot_iterator_buf<sigc::internal::signal_emit1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >, bool>::operator*() const (this=<synthetic pointer>) at /app/include/sigc++-2.0/sigc++/signal.h:302
#17 ArdourCanvas::Item::EventAccumulator<bool>::operator()<sigc::internal::slot_iterator_buf<sigc::internal::signal_emit1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >, bool> >(sigc::internal::slot_iterator_buf<sigc::internal::signal_emit1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >, bool>, sigc::internal::slot_iterator_buf<sigc::internal::signal_emit1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >, bool>) (last=..., first=..., this=<synthetic pointer>) at ../libs/canvas/canvas/item.h:239
#18 sigc::internal::signal_emit1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >::emit(sigc::internal::signal_impl*, _GdkEvent* const&) (_A_a1=@0x7fffffffd068: 0x7fffffffd0f0, impl=0x5555584acde0) at /app/include/sigc++-2.0/sigc++/signal.h:849
#19 sigc::signal1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >::emit(_GdkEvent* const&) const (_A_a1=@0x7fffffffd068: 0x7fffffffd0f0, this=<optimized out>) at /app/include/sigc++-2.0/sigc++/signal.h:2797
#20 sigc::signal1<bool, _GdkEvent*, ArdourCanvas::Item::EventAccumulator<bool> >::operator()(_GdkEvent* const&) const (_A_a1=@0x7fffffffd068: 0x7fffffffd0f0, this=<optimized out>) at /app/include/sigc++-2.0/sigc++/signal.h:2805
#21 ArdourCanvas::GtkCanvas::deliver_event(_GdkEvent*) (this=<optimized out>, event=<optimized out>) at ../libs/canvas/canvas.cc:772
#22 0x00007ffff6f6fd1a in non-virtual thunk to ArdourCanvas::GtkCanvas::on_button_release_event(_GdkEventButton*) () at ../libs/canvas/canvas/canvas.h:251
#23 0x00007ffff5d27df2 in Gtk::Widget_Class::button_release_event_callback(_GtkWidget*, _GdkEventButton*) (self=0x555557ad7060, p0=0x5555591eeb20) at widget.cc:4673
#24 0x00007ffff66148e1 in _gtk_marshal_BOOLEAN__BOXED (closure=0x555557098b00, return_value=0x7fffffffd330, n_param_values=<optimized out>, param_values=0x7fffffffd390, invocation_hint=<optimized out>, marshal_data=<optimized out>) at gtkmarshalers.c:86
#25 0x00007ffff6a82349 in g_closure_invoke () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#26 0x00007ffff6a95513 in signal_emit_unlocked_R () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#27 0x00007ffff6a9c22b in g_signal_emit_valist () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#28 0x00007ffff6a9cab3 in g_signal_emit () at /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
#29 0x00007ffff673f974 in gtk_widget_event_internal (widget=widget@entry=0x555557ad7060, event=event@entry=0x5555591eeb20) at gtkwidget.c:5010
#30 0x00007ffff673fc98 in IA__gtk_widget_event (widget=widget@entry=0x555557ad7060, event=event@entry=0x5555591eeb20) at gtkwidget.c:4807
#31 0x00007ffff6612d54 in IA__gtk_propagate_event (widget=0x555557ad7060, event=0x5555591eeb20) at gtkmain.c:2490
#32 0x00007ffff661322b in IA__gtk_main_do_event (event=0x5555591eeb20) at gtkmain.c:1685
#33 IA__gtk_main_do_event (event=<optimized out>) at gtkmain.c:1490
#34 0x00007ffff6466fd9 in gdk_event_dispatch (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at gdkevents-x11.c:2403
#35 0x00007ffff698e291 in g_main_context_dispatch () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#36 0x00007ffff698e538 in g_main_context_iterate.constprop () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#37 0x00007ffff698e853 in g_main_loop_run () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#38 0x00007ffff6611fa2 in IA__gtk_main () at gtkmain.c:1257
#39 0x00007ffff6dcb7af in Gtkmm2ext::UI::run(Receiver&) (this=this@entry=0x555557004ba0, old_receiver=...) at ../libs/gtkmm2ext/gtk_ui.cc:310
#40 0x0000555555aac092 in main(int, char**) (argc=<optimized out>, argv=<optimized out>) at ../gtk2_ardour/main.cc:422