gobjectmodule.c contains these lines:

#define REGISTER_TYPE(d, type, name) \
    type.ob_type = &PyType_Type; \
    type.tp_alloc = PyType_GenericAlloc; \
    type.tp_new = PyType_GenericNew; \
    ...

I'm not sure they are needed at all (except for 'ob_type' assignment), but some '.c' files actively set 'tp_new' to some custom function.  And fail because the custom function is not called when it should be.

The result is (at least) that pickling/unpickling enumeration values doesn't work:

>>> import pickle, gtk
>>> gtk.JUSTIFY_RIGHT == pickle.loads (pickle.dumps (gtk.JUSTIFY_RIGHT, -1))
__main__:1: Warning: comparing different enum types: GtkJustification and (null)
False

Attached patch fixes 'tp_new' and 'tp_alloc' overrides.  As a side-effect, pickling/unpickling is back to normal:

>>> import pickle, gtk
>>> gtk.JUSTIFY_RIGHT == pickle.loads (pickle.dumps (gtk.JUSTIFY_RIGHT, -1))
True