"Index out of range" situation in QMainWindowLayout class

qmainwindowlayout.cpp, line 1551:
fixToolBarOrientation(widgetItem, currentGapPos.at(1)); << currentGapPos can be empty here

to repeat this situation:
create QDockWidget, using some existing QMainWindow object as parent.. execute the following methods of created QDockWidget: setFloating(true); setFeatures(0); setAllowedAreas(Qt::NoDockWidgetArea); show();
then try to grag this QDockWidget onto QMainWindow and release mouse..