Window is transparent when moved to external monitor

When a simple/blank QML application is created and launched on mac book and then moved to an external monitor then the window turns blank.

Prerequisite:
Set application to use software renderer by setting:

QQuickWindow::setSceneGraphBackend( QSGRendererInterface::Software); in main.cpp

Steps:

1) Disconnect external monitor

2) Lanch application
3) Connect external monitor
4) Move applicaiton window to external monitor.

Result:
Application window turns transparent.