PhongAlphaMaterial looks wrong

There seems to be an issue with PhongAlphaMaterial. This can be seen for example with Audio Visualizer Example. In the example there is a circleEntity (Visualizer.qml) that should show a 'reflection' for the bars. The correct visualization is shown in documentation (https://doc.qt.io/qt-5/qt3d-audio-visualizer-qml-example.html) and in attached (correctPhongAlphaMaterial.png) picture. The wrongPhongAlphaMaterial picture shows how it is currently.

If the PhongAlphaMaterial is changed to PhongMaterial then the circle is shown on top of the bars as it should so there's clearly something wrong with the PhongAlphaMaterial.