Native Window Graphics Overwriting [5.10.0 regression]

First of all, this is a regression compared to past version (<= 5.9.1)

I have a Qt window that hosts a native NSView child, that covers almost all the surface.

When the Qt Window is activated (mouse click), or deactivated (click on another window), then the window becomes blank. I mean, the native window's graphics are somehow overwritten. This is weird, because this native NSView is an opaque nsview. If I click in the window to update some of the native graphics, these graphics appear again, out of the blank surface (just to prove the native nswindow is still there and properly sized).

I have seen that many changes have occurred in qcocoawindow.mm, but also most importantly in QCocoaBackingStore::flush, but I could not figure out where the problem comes from.

I doubt I can create a demo application, but maybe you could give me an idea where I should look in the 5.10.0 changes, ie. where the cause of this could be.

Thanks