Inconsistency in dictionary behaviour: dict(dict) not calling __setitem__

[Almad]

Hello,

I discovered this behaviour in dictionary which I find confusing. In
SneakyLang, I've tried to extend dictionary so it visits another class
after something is added:

class RegisterMap(dict):
    def __setitem__(self, k, v):
        dict.__setitem__(self, k,v)
        self[k].visit_register_map(self)


However, when constructing dictionary with dictionary in constructor
like d = RegisterMap({'k':'v'}), __setitem__ is not called, so
workaround is needed:

class RegisterMap(dict):
    def __init__(self, *args, **kwargs):
        dict.__init__(self, *args, **kwargs)
        for k in self:
            self.__after_add(k)

    def __after_add(self, k):
        self[k].visit_register_map(self)

    def __setitem__(self, k, v):
        dict.__setitem__(self, k,v)
        self.__after_add(k)


What is the reason for this behavior? Am I doing something wrong and
better approach is needed? Or should this be considered as minor bug in
Python? (tried this only in 2.4 so far)

Thank You,

Almad