QToolButton.setMenu() leaks and crashes

import sys
from PySide2.QtWidgets import *

a = QToolButton()
b = QMenu()
print sys.getrefcount(b) # =2
a.setMenu(b)
print sys.getrefcount(b) # =3
a.setMenu(None)
print sys.getrefcount(b) # =3?

del a
del b
# QMenu::~QMenu() is not invoked