QCompleter doesn't emit highlighted() or activated() if the completion model has changed

With Qt 4.5 the attached code inserted the highighted or activated item into the line edit, and in case of activation, the returnPressed signal was also emitted. After moving to Qt 4.6 this code doesn't work anymore. It's still possible to navigate through the completion list, but neither highlighting nor activating an item doesn't result in the behavior mentioned above. Inserting some debug output into the corresponding slots hints that possibly the highlighted() or activated() signals don't get emitted.