Inconsistent handling of "close" w/QWindows

Generally if you have a QMainWindow containing a QWindow (e.g. by using QWidget::createWindowContainer()):
 
  - if you call QMainWindow::close(), the QWindow receives QEvent::Hide and does the right thing - i.e. I can show it again and everything is ok
  - if you click the close button in the title bar, the QWindow receives QEvent::Close which (might!) call QWindow::destroy()
 
Tried on macOS 10.12.6 with Qt 5.11.2 and Qt 5.12 from git, and Windows 7 with Qt 5.11.2.
 
Expectation
For a window containing a QWindow (in a widget), I would expect clicking on the close button in the title bar to do the same thing as calling close().

Example
There are several issues here.

• Run the example
• click "Show Raster"
• this will create and show a window using QRasterWindow & you should see "_RasterContents QPlatformSurfaceEvent(surfaceEventType=SurfaceCreated)"
• click "Close Raster"
• this will close the window by calling "close()"
• click "Show Raster" - this will show it again - all good!

Now:

• click the close button on the Raster window's title bar
• we now get "_RasterContents QPlatformSurfaceEvent(surfaceEventType=SurfaceAboutToBeDestroyed)"? (Problem #1 - why is this happening?)
• but I don't think anything is actually destroyed...
• showing it again works...

Now let's do the same with the 3D example:

• click "Show 3D"
• this will create and show a window using QRasterWindow & you should see "_3DContents QPlatformSurfaceEvent(surfaceEventType=SurfaceCreated)"
• click "Close 3D"
• this will close the window by calling "close()"
• click "Show 3D" - this will show it again - all good!

Now:

• click the close button on the 3D window's title bar
• now we get "_3DContents QPlatformSurfaceEvent(surfaceEventType=SurfaceAboutToBeDestroyed)"
• click "Show 3D"
• contents are gone! (or crashes on Windows?) (Problem #2 - why are my contents gone?)
• There is a slight difference here on macOS between 5.11 and 5.12. With 5.11 I get a white background, with 5.12 I get a grey background.

Bonus problem
With the raster one, (at least on macOS), when the window is shown and I command-tab away and then back, the contents are not updated until I resize the window. (Problem #3 - it should be updated properly)

(I will attach the example code after I have a bug number.)