Python bindings and GObject derived class destructor

Tero found interesting memory issue with Midgard2 Python bindings. The code he presented is very simple:

import _midgard as midgard

while True:
    qb = midgard.query_builder ("midgard_host")

Guess, what happens. Memory usage grows up till your machine is frozen. I started to investigate this issue and reproduced problem with different case:

import gobject

class my_memory_test (gobject.GObject):
    def __init__ (self):
        gobject.Object.__init (self)

while True:
    mmt = my_memory_test()

This script kills machine perfectly too.

As Python bindings for Midgard depends on GObject bindings I started to invent own destructor. Finally solution is plain and simple. Instead of derived destructor (the one assigned to tp_dealloc), I added new one:

void
_py_midgard_gobject_destructor (PyObject *self)
{
    PyGObject *pygobj = (PyGObject *) self;
    if (pygobj->obj && G_IS_OBJECT (pygobj->obj))
            g_object_unref (pygobj->obj);

    PyObject_GC_Del (self);
}

Now the question is: does derived class destructor inherits parent class' one if explicitly defined as none? Basic debug statements clearly showed that parent's destructor is invoked but why memory usage grew till death?