Setting the Qt::WA_Maemo5AutoOrientation flag in a main window doesn't produce any effect when the application is first started. After some interaction like accessing the view menu or minimizing the application, the auto rotation starts to work.

The problem can be reproduced with the example application found here:

http://doc.qt.nokia.com/qt-maemo-4.6/maemo5-rotation.html

Compile and run the application on N900 (it will start in autorotation mode by default). Try to rotate the device after startup: nothing happens. Minimize the application and bring it back to the foreground, then rotate the device: auto rotation works.

Note: this was tested by starting the application remotely from Qt creators. I haven't tried what happens if the application is installed as a debian package.