Creating MDI window from dock widget causes all MDI windows become active

Steps to reproduce. From my 1st MDI window I create a dock widget with tree widget in it. When user double-click an item in this tree widget,1st mdi window slot, connected to double-click signal creates new MDI window. All MDI windows become active in this case and I can't catch windowStateChanged signal. If I create MDI window by clicking a button in first mdi window - all become normal again. Code to create mdi window is the same in both cases:

  mdiArea->addSubWindow(newMDI);
  newMDI->setMainWindow(this);
  newMDI->show();
  newMDI->raise();
  mdiArea->setActiveSubWindow(newMDI);

"this" is main window. Could this happen because dock widget has focus or smth like this on mdi creation?

More info:
http://stackoverflow.com/questions/36332562/all-mdi-windows-are-active
https://forum.qt.io/topic/65615/all-mdi-windows-are-active