[Reg: 5.6.1->5.6.2] Windows/Software GL: When resizing window the content isn't refreshed

When resizing a window with Qt::AA_UseSoftwareOpenGL enabled the window content isn't refreshed properly.
The issue can be seen after applying commit "Windows QPA: Improve workaround for non-Areo theme GL rendering." 6086c81e4d999d88ce4d412 https://codereview.qt-project.org/#/c/159429/ which disabled use of InvalidateRect() in Windows QPA.

Steps to reproduce the issue:
1. Run attached test application
2. Resize window

Expected outcome:
Inside of the window is refreshed properly and no trail of window resize can be seen.

Actual outcome:
Resizing window leaves ghost image inside of it and it's not refreshed properly.
See the attached screenshots.

Reproduces at least on:
OS : Windows 10 (64bit)
Compiler: Visual Studio 2015