Env: Ubuntu 14.04LTS
Gtk:
lvtk-gtkui-1 lvtk-gtkui - LV2 Toolkit GtkUI
gtkmm-2.4 gtkmm - C++ binding for the GTK+ toolkit
gtk+-unix-print-2.0 GTK+ - GTK+ Unix print support
gtk+-2.0 GTK+ - GTK+ Graphical UI Library (x11 target)
gtk+-x11-2.0 GTK+ - GTK+ Graphical UI Library (x11 target)
Qt: Qt5.9.2

Reproduce:

1. build example : recipebrowser
2. run recipebrowser.
3. Rapidly drog the mainwindow frame, so that the mainwindow do resize rapidly.

Test result: Program received signal SIGSEGV, Segmentation fault.
Backtrack:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fff75ef4700 (LWP 30824)]
0x00007fffee4429cb in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5WebEngineCore.so.5
(gdb) where
#0 0x00007fffee4429cb in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5WebEngineCore.so.5
#1 0x00007fffee442d0d in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5WebEngineCore.so.5
#2 0x00007fffee443472 in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5WebEngineCore.so.5
#3 0x00007fffee4496d0 in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5WebEngineCore.so.5
#4 0x00007fffee466d28 in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5WebEngineCore.so.5
#5 0x00007ffff5736f50 in QQuickWindowPrivate::updateDirtyNode(QQuickItem*) () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Quick.so.5
#6 0x00007ffff57375fd in QQuickWindowPrivate::updateDirtyNodes() () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Quick.so.5
#7 0x00007ffff5738722 in QQuickWindowPrivate::syncSceneGraph() () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Quick.so.5
#8 0x00007ffff56e8eb5 in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Quick.so.5
#9 0x00007ffff56eac6f in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Quick.so.5
#10 0x00007ffff56eeb5c in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Quick.so.5
#11 0x00007ffff652270a in ?? () from /home/user/Qt/5.9.2/gcc_64/lib/libQt5Core.so.5
#12 0x00007ffff4fa9184 in start_thread (arg=0x7fff75ef4700) at pthread_create.c:312
#13 0x00007ffff5c82ffd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

PS : The example that use webengineview has the same problem.