title: Can't use QMainWindow after opened a QDialog (Qt)
body: <p>In my program I have the following problem: After I opened a <code>QDialog</code> from <code>QMainWindow</code>, I can't use the <code>QMainWindow</code>, only if I close the <code>QDialog</code> first.
  Is there a solution for this? </p>
  
  <p>Thank you,</p>
  
  <p>Mate</p>