A blocked child window freezes parent window too

Reproducer attached. One needs to build "Child" first, winqtdeployqt it, and then run "Parent". It is going to launch "Child" and then embed the window in itself.

"Child" has a button which blocks the main thread by clicking. So when "Child" is blocked, "Parent" is unresponsive too.

I've tested both 6.7 and 6.8, starting "Child" detached or non-detached. I've also tried to embed "Child" into a QML Window (https://www.qt.io/blog/window-embedding-in-qt-quick). Nevertheless, none of those makes any difference. And it is said that the problem does not happen on Linux. So I tend to think it's a Windows issue but can't be sure.