Using Screen class to calculate/set width and height brings strange behavior when the app returns to foreground

With the code below, the app doesn't fill the entire screen when it comes back from background to foreground. ( qtbug81027_ipad_screenshot.png )

main.cpp

QQuickView view;
view.setResizeMode(QQuickView::SizeRootObjectToView);
...

main.qml

Rectangle {
    id: app
    visible: true

    property var i : Screen.width >= 0 ? 1 : 1

    width: 640 * i
    height: 480 * i
 ...
}

The same behavior occurs at least with Screen.height and Screen.logicalPixelDensity.

How to reproduce:
1. Run the sample code (qtbug81027.zip) on iPad
2. Put the app to the background (by pressing home button)
3. Bring the app to foreground

Result :
The app does not fill the entire screen (qtbug81027_ipad_screenshot.png)

Workaround ?
Modify var to some other type e.g. int or real enables the app to fill the entire screen when it returns to foreground.