QInputDialog shifting its position

[cleanzero]

Hi all,
I wrote a simple code where I ask the user to input some values during a for loop using a QInputDialog.

for(i=0;i<3;++i)
    {
        s = QInputDialog::getText(this,tr("Insert a number"),tr("Input"),QLineEdit::Normal,
                                  NULL,&ok);
        if(s!=NULL)
            ui->listWidget->addItem(s);
    }

for(i=0;i<3;++i)
    {
        s = QInputDialog::getText(this,tr("Insert a number"),tr("Input"),QLineEdit::Normal,
                                  NULL,&ok);
        if(s!=NULL)
            ui->listWidget->addItem(s);
    }

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Problem is that after each iteration the Dialog window shifts a bit along the x and y direction. Why ? How can I fix its position ?