Ok, here are some code snippets from the application. . .

In MDI MainWindow:
Qt Code: 
  1. void MainWindow::createMdiPrevQSOs()
  2. {
  3.     // show the window
  4.     mdiPrev = new mdiPrevQSOs;
  5.     mdiArea->addSubWindow(mdiPrev);
  6.     mdiPrev->show();
  7. }
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long after creation:
Qt Code: 
  1. void MainWindow::slotUpdatePrev()
  2. {
  3.          QList<QMdiSubWindow *> windows = mdiArea->subWindowList();
  4.          foreach (QMdiSubWindow *window, mdiArea->subWindowList())
  5.          {
  6.                  if (window->windowTitle().startsWith(tr("Previous"),Qt::CaseInsensitive))
  7.                  {
  8.                      mdiPrevQSOs *child = qobject_cast<mdiPrevQSOs *>(window);
  9.                      if (child->findPrev()) // (debug shows seg fault previous step is here)
  10.                      {
  11.                          . . .
  12.                      }
  13.                 }
  14.          }
  15.          . . .
  16. }
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the MDISubWindow has a list Widget that is filled by the called function.

mdiPrevQSOs constructor:
Qt Code: 
  1. mdiPrevQSOs::mdiPrevQSOs(QWidget *parent) : QDialog(parent)
  2. {
  3.          setAttribute(Qt::WA_DeleteOnClose);
  4.          . . .
  5.          widget = new QWidget(this);
  6.          widget->setObjectName(QString::fromUtf8("widget"));
  7.          . . .
  8.          listView = new QTreeView(widget);
  9.          listView->setObjectName(QString::fromUtf8("listView"));
  10. }
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the public function called:
Qt Code: 
  1. bool mdiPrevQSOs::findPrev()
  2. {
  3.          . . .
  4.          // create a query . . .
  5.          // create a QStandardItemModel for the tree view. . .
  6.          // fill the model with data from the query . . .
  7.          . . .
  8.          // (this line crashes with a seg fault)
  9.          listView->setModel(s_model);   // the tree view created in the constructor
  10.      . . .
  11. }
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