QSlider in toolbar drawn incorrectly when setUnifiedTitleAndToolBarOnMac( true )

If:

setUnifiedTitleAndToolBarOnMac( true );

Then QSlider in toolbar shows visual artefacts when moved (see attached).

Works ok on Qt 5.1.2.3 and Qt 5.13.1 or if set setUnifiedTitleAndToolBarOnMac( false ) on 5.12.5 or 5.12.7.

#include "MainWindow.h"
#include <QSlider>

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)

{ setupUi(this); setUnifiedTitleAndToolBarOnMac( true ); QSlider* zoomSlider = new QSlider( this ); zoomSlider->setOrientation( Qt::Horizontal ); QAction* zoomSliderAction = mainToolBar->addWidget( zoomSlider ); zoomSliderAction->setIconText( "Zoom slider" ); }

Full code attached.