Making child widget native causes TLW to cover whole screen

Given a widget hierarchy like this:

TLW
|
+--Child

calling winId() on the child before the TLW is shown causes the TLW to be resized to cover the whole screen.

Environment

Qt: Built from source, qt-s60-public/4.7 commit 700ba679
Device: N8, wk26 RnD image

Steps to reproduce

This can be reproduced using the attached test app videooverlay_QTBUG-12605_1.zip.

The attached logs were created in the above environment using the following command line options:

alien.log

videooverlay.exe -video none -overlay childwidget

native.log

videooverlay.exe -video none -overlay nativechildwidget

Expected behaviour

Calling winId() on the child widget has no effect on the geometry of either the TLW or the child widget.

Observed behaviour

Calling winId() on the child widget causes the TLW to be resized to cover the whole screen (360x640).