thanks, but that was the last thing I tried yesterday.
Still, it doesn't work. (see output below)

Qt Code: 
  1. bool PluginConfig::applyChanges()
  2. {
  3.     qDebug() << __FILE__ << __LINE__ << __FUNCTION__ << m_wdgtStack->currentIndex() << m_wdgtStack->count();
  4.     ConfigWidget* wdgt = qobject_cast<ConfigWidget*>(m_wdgtStack->currentWidget());
  5.     if(wdgt)
  6.         return wdgt->applyChanges();
  7.     else{
  8.         qDebug() << __FILE__ << __LINE__ << __FUNCTION__ << "no widget in stack?";
  9.         wdgt = static_cast<ConfigWidget*>(m_wdgtStack->widget(m_wdgtStack->currentIndex()));
  10.         if(wdgt)
  11.             return wdgt->applyChanges();
  12.         else
  13.         return false;
  14.     }
  15. }
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Qt Code: 
  1. configdialog.cpp 73 apply
  2. pluginconfig.cpp 35 applyChanges 0 3
  3. pluginconfig.cpp 40 applyChanges no widget in stack?
  4. alsaconfig.cpp 41 applyChanges
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I hadforgotten to include the Q_OBJECT
but after I included it I run a
$>qmake -recursive; make clean; clear; make
just to make sure.

Any other ideas?

I read a bit in "Thinking in C++" and if I got that right, the static_cast<> only allows me to downcast within the hierarchy. That would be alright then.