Custom sorting of QStandardItem cannot be implemented

When QStandardItem.__lt__ (corresponding to operator<) is implemented, it is never called. When using PyQt5, the attached code outputs

before sort:
Item(1)
Item(0)
__lt__(Item(0), Item(1)) called
after sort:
Item(0)
Item(1)

whereas for PySide the output is

before sort:
Item(1)
Item(0)
after sort:
Item(1)
Item(0)