QwtPlotOpenGLCanvas plot window disappears then reappears

I noticed after upgrading to Qt6.4 from Qt5.12 that the first time you set a QwtPlotOpenGLCanvas to a plot the window the plot lives in hides then shows. You can see this behavior in the refreshtest example, when you click the OpenGL checkbox the entire refreshtest window will disappear and reappear, after that you can check and uncheck the OpenGL box and it will work as expected. Is there any way to prevent this behavior?

Could you please create a bug report here: https://sourceforge.net/p/qwt/bugs/
I will spend a couple of days on bug fixing in the next weeks and will have a look at it too.

Uwe