Regression: QWebEngineView + WM_NCCALCSIZE + HighDPI screen painting failure

I have tested this issue using small application attached to bug https://bugreports.qt.io/browse/QTBUG-40578
I just added few strings to MainWindow constructor to that app which makes this bug appear:

QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
...
QWebEngineView *w = new QWebEngineView(this);

How to reproduce bug:

• Use laptop 4K screen (200%-250% scale ratio in Windows settings)
• Run app
• Toggle F11 to switch app between frameless and non-frameless mode
• You will see that the yellow app window painted incorrectly in frameless mode

Then comment string above, and uncomment string //QWidget *w = new QWidget(this);
Test again - and you will see that bug does not appear.

Seems when webengine added to mainwindow, inner widgets painted with some offset equal titlebar height

Test app - qtbug40578-new.zip
Screen capture - 2018-11-14_21-32-29.mp4