I found this issue when I was trying to run the Multitouch Dials example which ships with Qt SDK.
I found that I can rotate multiple knobs simultaneously only once. Once any of the dial is touched/mousepressed Qt creates native window for that. Each knob's is set to accept touch event. Also QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings) is done at application level.

After delving into Qt code I found that in QWidget::winId(), it does setAttribute(Qt::WA_NativeWindow) even if the Qt::AA_DontCreateNativeWidgetSiblings attribute is set for the application.
I have tested that this issue is fixed if I put check
if(QCoreApplication::testAttribute(Qt::AA_DontCreateNativeWidgetSiblings)==false)
before that->setAttribute(Qt::WA_NativeWindow); is called in QWidget::winId(). I am not sure if this is correct fix but it works for me.

Thanks