2. Исчезла прозрачность объектов.
В Assistant в статье Porting to Qt 3.x :
Transparent widgets
In Qt 2.x, the AutoMask property was used to obtain a transparent-looking widget. In general, this approach is slow and processor hungry. Qt 3.0 uses the BackgroundOrigin which provides vastly improved performance and more flexibility in most cases. The few classes for which the AutoMask property is still the best approach are QCheckBox, QComboBox, QPushButton, QRadioButton and QTabWidget.
3. В запущенном потоке postEvent() выдает сообщение, что поток не проинициализирован, соответственно ничего не передается.
Попробуй через QApplication::postEvent().
void QThread::postEvent ( QObject * receiver, QEvent * event ) [static]
This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.
Use QApplication::postEvent() instead.