When QListWidget's items are changed it can crash if scrollbars are displayed automatically. It happens when the necessary view area is closed to the QListWidget's area and it is closed to the limit for use or not use scrollbar(s).
See the example. If the size of the GUI is the appropriate size, it crashes when items are changed. The appropriate size is around as seen on the picture. After set this size the second button press crashes the program with Qt 4.8.4.
With 5.1 it only freezes for some seconds.