QDialog subclass does not paint on second show. Moving scrollbar in the QDialog subclass then causes ASSERT failure in QWidget::mapTo(const QWidget *parent, const QPoint &pos): "parent must be in parent hierarchy", file kernel/qwidget.cpp, line 4253

In the simple working example attached, for the second time the TestDialog subclass of QDialog is shown it does not receive a paint event.  If I then resize the TestDialog it is painted but then moving either of its scrollbars (its layout contains a QScrollArea widget) will then cause the following assertion in QWidget to fail:

ASSERT failure in QWidget::mapTo(const QWidget *parent, const QPoint &pos): "parent must be in parent hierarchy", file kernel/qwidget.cpp, line 4253
./Main.sh: line 18: 21498 Aborted (core dumped) $val ./Main

I get this bug with a selection of Qt5 versions >=5.11.1. The version I am currently working with is 5.12.4.

This bug does not occur with Qt5 versions <=5.11.0 and also 4.8.7.

Here is the backtrace:

[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Core was generated by `./Main'.
Program terminated with signal SIGABRT, Aborted.
#0 0x00007f666f400207 in raise () from /lib64/libc.so.6
[Current thread is 1 (Thread 0x7f6671557780 (LWP 21498))]
Missing separate debuginfos, use: debuginfo-install bzip2-libs-1.0.6-13.el7.x86_64 dbus-libs-1.10.24-13.el7_6.x86_64 devtoolset-4-elfutils-libelf-0.166-1.el7.x86_64 devtoolset-4-elfutils-libs-0.166-1.el7.x86_64 expat-2.1.0-10.el7_3.x86_64 fontconfig-2.13.0-4.3.el7.x86_64 freetype-2.8-12.el7_6.1.x86_64 glib2-2.56.1-4.el7_6.x86_64 glibc-2.17-260.el7_6.5.x86_64 libICE-1.0.9-9.el7.x86_64 libSM-1.2.2-2.el7.x86_64 libX11-1.6.5-2.el7.x86_64 libXau-1.0.8-2.1.el7.x86_64 libXcursor-1.1.14-8.el7.x86_64 libXext-1.3.3-3.el7.x86_64 libXfixes-5.0.3-1.el7.x86_64 libXrender-0.9.10-1.el7.x86_64 libattr-2.4.46-12.el7.x86_64 libcap-2.22-9.el7.x86_64 libgcc-4.8.5-28.el7_5.1.x86_64 libgcrypt-1.5.3-14.el7.x86_64 libgpg-error-1.12-3.el7.x86_64 libicu-50.1.2-17.el7.x86_64 libpng-1.5.13-7.el7_2.x86_64 libselinux-2.5-11.el7.x86_64 libstdc++-4.8.5-28.el7_5.1.x86_64 libuuid-2.23.2-43.el7_4.2.x86_64 libxcb-1.13-1.el7.x86_64 libxkbcommon-0.7.1-1.el7.x86_64 libxkbcommon-x11-0.7.1-1.el7.x86_64 lz4-1.7.5-2.el7.x86_64 pcre-8.32-17.el7.x86_64 systemd-libs-219-62.el7_6.6.x86_64 xz-libs-5.2.2-1.el7.x86_64 zlib-1.2.7-18.el7.x86_64
(gdb) bt
#0 0x00007f666f400207 in raise () from /lib64/libc.so.6
#1 0x00007f666f4018f8 in abort () from /lib64/libc.so.6
#2 0x00007f667026d723 in qt_message_fatal (context=..., message=...) at global/qlogging.cpp:1904
#3 0x00007f667026e210 in QMessageLogger::fatal (this=this@entry=0x7ffd84377e60,
msg=msg@entry=0x7f66705628b0 "ASSERT failure in %s: \"%s\", file %s, line %d") at global/qlogging.cpp:888
#4 0x00007f6670268917 in qt_assert_x (
where=where@entry=0x7f66711c6ab8 "QWidget::mapTo(const QWidget *parent, const QPoint &pos)",
what=what@entry=0x7f66711c6a90 "parent must be in parent hierarchy",
file=file@entry=0x7f66711bfd49 "kernel/qwidget.cpp", line=line@entry=4253) at global/qglobal.cpp:3216
#5 0x00007f6670e36787 in QWidget::mapTo (this=this@entry=0x2005900, parent=parent@entry=0x2005b00, pos=...)
at kernel/qwidget.cpp:4252
#6 0x00007f6670e17b66 in QWidgetBackingStore::qt_flush (widget=widget@entry=0x2005900, region=...,
backingStore=0x2091f30, tlw=0x2005b00, widgetTextures=<optimized out>,
widgetBackingStore=widgetBackingStore@entry=0x20878c0) at kernel/qwidgetbackingstore.cpp:124
#7 0x00007f6670e18e77 in QWidgetBackingStore::flush (this=this@entry=0x20878c0, widget=widget@entry=0x0)
at kernel/qwidgetbackingstore.cpp:1468
#8 0x00007f6670e18eec in QWidgetBackingStore::endPaint (this=this@entry=0x20878c0, cleaned=...,
backingStore=<optimized out>, beginPaintInfo=beginPaintInfo@entry=0x7ffd843780b0) at kernel/qwidgetbackingstore.cpp:363
#9 0x00007f6670e1a471 in QWidgetBackingStore::doSync (this=this@entry=0x20878c0) at kernel/qwidgetbackingstore.cpp:1426
#10 0x00007f6670e1a891 in QWidgetBackingStore::sync (this=0x20878c0) at kernel/qwidgetbackingstore.cpp:1204
#11 0x00007f6670e36b72 in QWidgetPrivate::syncBackingStore (this=this@entry=0x20828a0) at kernel/qwidget.cpp:1961
#12 0x00007f6670e4f103 in QWidget::event (this=0x2005b00, event=0x205dba0) at kernel/qwidget.cpp:9264
#13 0x00000000004036a0 in TestDialog::event (this=0x2005b00, e=0x205dba0) at TestDialog.cpp:32
#14 0x00007f6670e09f4a in QApplicationPrivate::notify_helper (this=this@entry=0x1f4bcb0, receiver=receiver@entry=
0x2005b00, e=e@entry=0x205dba0) at kernel/qapplication.cpp:3737
#15 0x00007f6670e13161 in QApplication::notify (this=0x7ffd84378b90, receiver=0x2005b00, e=0x205dba0)
at kernel/qapplication.cpp:3687
#16 0x00007f667043e84d in QCoreApplication::notifyInternal2 (receiver=0x2005b00, event=0x205dba0)
--Type <return> to continue, or q <return> to quit--quit
at kernel/qcoreapplicationQuit
(gdb) quit

Here are the events for the QDialog subclass called TestDialog:

TestDialog::event QEvent::Type::WindowTitleChange
TestDialog::event QEvent::Type::ChildAdded
TestDialog::event QEvent::Type::ChildAdded
TestDialog::event QEvent::Type::PlatformSurface
TestDialog::event QEvent::Type::WinIdChange
TestDialog::event QEvent::Type::WindowIconChange
TestDialog::event QEvent::Type::Polish
TestDialog::event QEvent::Type::ChildPolished
TestDialog::event QEvent::Type::Move
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Show    [First show event]                 
TestDialog::event QEvent::Type::Move
TestDialog::event QEvent::Type::CursorChange
TestDialog::event QEvent::Type::ShowToParent
TestDialog::event QEvent::Type::FocusIn
TestDialog::event QEvent::Type::PolishRequest
TestDialog::event QEvent::Type::LayoutRequest
TestDialog::event QEvent::Type::UpdateLater
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Paint    [Paint for first show event]
TestDialog::event QEvent::Type::WindowActivate
TestDialog::event QEvent::Type::ActivationChange
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::Enter
TestDialog::event QEvent::Type::Leave
TestDialog::event QEvent::Type::Close
TestDialog::event QEvent::Type::WindowDeactivate
TestDialog::event QEvent::Type::ActivationChange
TestDialog::event QEvent::Type::Hide
TestDialog::event QEvent::Type::HideToParent
TestDialog::event QEvent::Type::Hide
TestDialog::event QEvent::Type::HideToParent
TestDialog::event QEvent::Type::PlatformSurface
TestDialog::event QEvent::Type::WinIdChange
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Show     [Second show event]
TestDialog::event QEvent::Type::Move
TestDialog::event QEvent::Type::PlatformSurface
TestDialog::event QEvent::Type::ShowToParent
TestDialog::event QEvent::Type::UpdateLater  [No paint after this until the resize]
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::WindowActivate
TestDialog::event QEvent::Type::ActivationChange
TestDialog::event QEvent::Type::Enter
TestDialog::event QEvent::Type::Leave
TestDialog::event QEvent::Type::Enter
TestDialog::event QEvent::Type::Leave
TestDialog::event QEvent::Type::WindowDeactivate
TestDialog::event QEvent::Type::ActivationChange
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Resize
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::WindowActivate
TestDialog::event QEvent::Type::ActivationChange
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::Enter
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Paint
TestDialog::event QEvent::Type::UpdateRequest
TestDialog::event QEvent::Type::Paint

The configure step for the Qt-5.12.4 install

debug="-debug"

cd qt-everywhere-src-5.12.4 && ./configure -v $debug \
-prefix $HOME/$install_dir \
-opensource \
-platform linux-g++ \
-qt-xcb \
-no-opengl \
-confirm-license \
-no-sql-db2 \
-no-sql-ibase \
-no-sql-mysql \
-no-sql-oci \
-no-sql-odbc \
-no-sql-psql \
-no-sql-sqlite \
-no-sql-sqlite2 \
-no-sql-tds \
-c+std c+11 \
-skip gamepad \
-skip activeqt \
-skip graphicaleffects \
-skip wayland \
-skip multimedia \
-skip location \
-skip webengine \
-skip webglplugin \
-skip webview \
-skip canvas3d \
-skip networkauth \
-skip datavis3d \
-skip 3d \
-skip declarative \
-skip sensors \
-skip speech \
-skip script \
-skip scxml \
-skip macextras \
-skip androidextras \
-skip quickcontrols \
-skip quickcontrols2 \
-skip translations \
-skip serialbus \
-skip serialport \
-skip connectivity \
-skip winextras \
-skip purchasing \
-no-cups && \
make && \
make install

$ uname -a
Linux UNKNOWN 3.10.0-693.11.1.el7.x86_64 #1 SMP Mon Dec 4 23:52:40 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-4/root/usr/libexec/gcc/x86_64-redhat-linux/5.3.1/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure -enable-bootstrap --enable-languages=c,c++,fortran,lto --prefix=/opt/rh/devtoolset-4/root/usr --mandir=/opt/rh/devtoolset-4/root/usr/share/man --infodir=/opt/rh/devtoolset-4/root/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --enable-plugin --with-linker-hash-style=gnu --enable-initfini-array --disable-libgcj --with-default-libstdcxx-abi=gcc4-compatible --with-isl=/builddir/build/BUILD/gcc-5.3.1-20160406/obj-x86_64-redhat-linux/isl-install --enable-libmpx --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 5.3.1 20160406 (Red Hat 5.3.1-6) (GCC)

Many Thanks,

Piers