Comment # 5 on bug 980474 from Martin Li��ka

I've got another back-trace:

#0  0x00007f297b2b4908 in raise () at /lib64/libc.so.6
#1  0x00007f297b2b5d5a in abort () at /lib64/libc.so.6
#2  0x00007f297bab5375 in g_assertion_message () at /usr/lib64/libglib-2.0.so.0
#3  0x00007f297bab540a in g_assertion_message_expr () at
/usr/lib64/libglib-2.0.so.0
#4  0x00007f297cfe480e in gtk_widget_get_frame_clock
(widget=widget@entry=0x1ff7370) at gtkwidget.c:5804
#5  0x00007f297cfe9f77 in gtk_widget_unrealize (widget=0x1ff7370) at
gtkwidget.c:5511
#6  0x00007f297cff561d in gtk_widget_unparent (widget=0x1ff7370) at
gtkwidget.c:4621
#7  0x00007f297ced7257 in gtk_notebook_remove_tab_label
(notebook=notebook@entry=0xd9e220, page=0x2022140, page=0x2022140) at
gtknotebook.c:4987
#8  0x00007f297ced7404 in gtk_notebook_remove (list=0xce51a0 = {...},
notebook=0xd9e220) at gtknotebook.c:5058
#9  0x00007f297ced7404 in gtk_notebook_remove (container=0xd9e220,
widget=0x1ff71f0) at gtknotebook.c:4222
#10 0x00007f297bd696d3 in g_cclosure_marshal_VOID__OBJECTv () at
/usr/lib64/libgobject-2.0.so.0
#11 0x00007f297bd669c4 in  () at /usr/lib64/libgobject-2.0.so.0
#12 0x00007f297bd809c8 in g_signal_emit_valist () at
/usr/lib64/libgobject-2.0.so.0
#13 0x00007f297bd810a2 in g_signal_emit () at /usr/lib64/libgobject-2.0.so.0
#14 0x00007f297cded2f5 in gtk_container_remove (container=0xd9e220,
widget=0x1ff71f0) at gtkcontainer.c:1905
#15 0x0000000000429e60 in terminal_window_move_screen (screen=0x2931810,
window=0xd94560) at terminal-window.c:3110
#16 0x0000000000429e60 in terminal_window_move_screen (source_window=0xd94560,
dest_window=0xd94560, screen=0x2931810, dest_position=-1) at
terminal-window.c:3137
#17 0x000000000041f11e in terminal_screen_drag_data_received (widget=<optimized
out>, context=0x201ba00, x=<optimized out>, y=<optimized out>,
selection_data=<optimized out>, info=<optimized out>, timestamp=82544882) at
terminal-screen.c:1917
#18 0x00007f297ceb0db7 in _gtk_marshal_VOID__OBJECT_INT_INT_BOXED_UINT_UINT
(closure=0xc7d7c0, return_value=<optimized out>, n_param_values=<optimized
out>, param_values=0x7ffd17448c40, invocation_hint=<optimized out>,
marshal_data=0x41ede0 <terminal_screen_drag_data_received>) at
gtkmarshalers.c:5525
#19 0x00007f297bd66795 in g_closure_invoke () at /usr/lib64/libgobject-2.0.so.0
#20 0x00007f297bd7862e in  () at /usr/lib64/libgobject-2.0.so.0
#21 0x00007f297bd80cca in g_signal_emit_valist () at
/usr/lib64/libgobject-2.0.so.0
#22 0x00007f297bd81555 in g_signal_emit_by_name () at
/usr/lib64/libgobject-2.0.so.0
#23 0x00007f297d00e7ed in gtk_drag_selection_received (widget=0xecaae0,
selection_data=0x7ffd17449530, time=82544882, data=0x2931810) at gtkdnd.c:1636
#24 0x00007f297bd66795 in g_closure_invoke () at /usr/lib64/libgobject-2.0.so.0
#25 0x00007f297bd78081 in  () at /usr/lib64/libgobject-2.0.so.0
#26 0x00007f297bd80cca in g_signal_emit_valist () at
/usr/lib64/libgobject-2.0.so.0
#27 0x00007f297bd81555 in g_signal_emit_by_name () at
/usr/lib64/libgobject-2.0.so.0
#28 0x00007f297cf2e173 in gtk_selection_retrieval_report
(info=info@entry=0x284db90, type=<optimized out>, format=<optimized out>,
buffer=<optimized out>, length=<optimized out>, time=time@entry=82544882) at
gtkselection.c:3031
#29 0x00007f297cf2fde1 in gtk_selection_convert (widget=0xecaae0,
selection=0xb6, target=0x84, time_=82544882) at gtkselection.c:1143
#30 0x00007f297d00ffde in gtk_drag_dest_drop (widget=0x2931810,
context=0x201ba00, x=1510, y=362, time=82544882) at gtkdnd.c:2151
#31 0x00007f297d00fc70 in _gtk_drag_dest_handle_event (callback=0x7f297d00ff20
<gtk_drag_dest_drop>, time=82544882, y=362, x=1510, info=0x2df8760,
context=0x201ba00, widget=0x2931810) at gtkdnd.c:1717
#32 0x00007f297d00fc70 in _gtk_drag_dest_handle_event
(toplevel=toplevel@entry=0xd94560, event=event@entry=0x21dab00) at
gtkdnd.c:1474
#33 0x00007f297cea934d in gtk_main_do_event (event=0x21dab00) at gtkmain.c:1896
#34 0x00007f297c9e14c5 in _gdk_event_emit (event=event@entry=0x21dab00) at
gdkevents.c:73
#35 0x00007f297ca0d5f2 in gdk_event_source_dispatch (source=<optimized out>,
callback=<optimized out>, user_data=<optimized out>) at gdkeventsource.c:367
#36 0x00007f297ba90227 in g_main_context_dispatch () at
/usr/lib64/libglib-2.0.so.0
#37 0x00007f297ba90458 in  () at /usr/lib64/libglib-2.0.so.0
#38 0x00007f297ba904fc in g_main_context_iteration () at
/usr/lib64/libglib-2.0.so.0
#39 0x00007f297c057d2d in g_application_run () at /usr/lib64/libgio-2.0.so.0
#40 0x0000000000413a65 in main (argc=1, argv=0x7ffd17449a38) at server.c:180

The issue happens always when I drag a tap from a window with multiple tabs and
drop it to a different monitor. That should cause creation of a new window.
Unfortunately, it's not much reproducible.