QMdiArea addSubWindow is not showing window when called from slot

[cranfss]

I am passing a MdiArea into a QWidget *child:

mdiArea = new QMdiArea;
setCentralWidget(mdiArea);
 
tabWidget = new QTabWidget;
QWidget *child = new parametertab(tabWidget, mdiArea);
 
mdiArea->addSubWindow(child); //this addSubWindow works as expected

mdiArea = new QMdiArea;
setCentralWidget(mdiArea);
	 
tabWidget = new QTabWidget;
QWidget *child = new parametertab(tabWidget, mdiArea);
    
mdiArea->addSubWindow(child); //this addSubWindow works as expected

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Inside the parametertab constructor, I can addsubwindow, but it does not work when I addsubwindow from within a slot. It does add the window to the subWindowList, and does not produce a warning. Any idea why it does not display the window?

class parametertab : public QWidget
{
 ...
 private slots:
    void runsim();
 ...
}
 
parametertab::parametertab(QTabWidget *tW, QMdiArea *ma, QWidget *parent)
   : QWidget(parent)
{
  ...
  QWidget *child = new QTextEdit;
  mdiArea->addSubWindow(child); //this works as expected
  ...
}
 
void parametertab::runsim()
{
  QWidget *child = new QTextEdit;
  mdiArea->addSubWindow(child); //does not show window?
}

class parametertab : public QWidget
{
 ...
 private slots:
    void runsim();
 ...
}

parametertab::parametertab(QTabWidget *tW, QMdiArea *ma, QWidget *parent)
   : QWidget(parent)
{
  ...
  QWidget *child = new QTextEdit;
  mdiArea->addSubWindow(child); //this works as expected
  ...
}

void parametertab::runsim()
{
  QWidget *child = new QTextEdit;
  mdiArea->addSubWindow(child); //does not show window?
}

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