Hiding a QToolTip while a drag and drop event sometimes interrupts program execution on X11 (bad window error)

Run the attached example code (modified from Qt example application /examples/draganddrop/draggableicons/) and execute following use case:

• drag one of the icon to top of the text label "Drop Icon here.This a simple example to test Drag drop issue."
  --> tool tip is displayed outside the widget window.
• continue dragging until the icon is on top of the tool tip and drop the icon

Error: sometimes the program execution interrupts.

• interruption happens after calling QToolTip::hideText(); on the attached dragwidget.cpp line 72
• Qt generates debug print "xdndHandleBadwindow returned true" from qapplication_x11.cpp: qt_x_errhandler() function
  Easy to reproduce on X11. Error is not reproduced on Windows.