Using signals derived from Mixin breaks slots in derived classes

import PySide2.QtCore as QtCore

class Mixin(object):
    mySignal = QtCore.Signal()
    def __init__(self, *args, **kwargs):
        super(Mixin,self).__init__(*args, **kwargs)
        
class Derived(Mixin, QtCore.QObject):
    echoSignal = QtCore.Signal(str)
    
    def __init__(self):
        super(Derived,self).__init__()
        self.echoSignal.connect(self.mySlot)
    
    def mySlot(self, v):
        print v + ' -> mySlot' 
 
def nopSlot():
    pass
 
obj = Derived()
obj.echoSignal.emit('emit1')
obj.mySignal.connect(nopSlot)  # This line breaks mySlot..
obj.echoSignal.emit('emit2')