Resizing window flickers with blue background

This is not a problem in 5.9.1, but in 5.9.2 snapshot and latest 5.9 branch on git.

Steps to reproduce:

1) Open Qt 3D example advancedcustommaterial.

2) Resize the window somewhat fast (in i.e. x-direction, increase and decrease width rapidly)

Sometimes the full content is filled with pure blue color.

Also, if you resize slowly (increasing width or height), the extra pixels become blue until redraw.