Maemo 5 auto-rotation: the application rotates back to landscape when a new window is opened

I have a Qt-based Maemo 5 application, and I'd like to enable automatic rotation of the user interface.

I have a QMainWindow, some QDialogs, and another QMainWindow that is a stacked window on top of the previous main window.
I did everything according to the description found in this page: http://doc.qt.nokia.com/qt-maemo-4.6/maemo5-rotation.html

I set the Qt::WA_Maemo5AutoOrientation on all of my windows, and connected to the desktop's

After launching the application, auto-rotation works for the first QMainWindow.
The issue is the following: If the app is in portrait mode, opening up a dialog or the other QMainWindow causes the UI to rotate back to landscape.
(If I tilt the device back and tilt it again, they rotate to portrait mode. If I open them from landscape mode and then tilt the N900, they will rotate again correctly. The only issue is opening them from portrait mode.)

Note that if I have the Phone application on the device open and set its orientation to "Portrait", it will work correctly.
Still, Qt should not require a certain setting of the Phone app to have autorotate working correctly.

I also uploaded a .zip file with this report which contains a small app to demonstrate the isse along with a readme file that contains the exact steps to reproduce it.
I'll also file a bug at bugs.maemo.org about the Phone application - it obviously shouldn't affect the behaviour of other applications.