Screen update causes flicker when objects are deleted and created

I'm developing a program where I redraw the scene at each simulation time step. Some objects in the scene are moved around, some are deleted and some are created. I use setRenderPolicy(Qt3DRender::QRenderSettings::OnDemand) to control when redraw happens and would expect there to be no flickering on the display. However there is clearly a delay in drawing the objects that are created and there is very obvious flicker on screen. I have created a simple example based on the basicshapes-cpp that illustrates the effect. It does not flicker all the time in the example probably because the redraw time is so quick but in my code the flicker is very bad (and the fact that it is flickering occasionally points at some underlying timing/caching issue).