Has threading in GTK w/ Python changed in PyGObject introspection?

I'm in the process of converting a program from PyGTK to PyGObject introspection for the first time and I've hit a roadblock with threading. I have a process that takes some time to complete, so I pop up a dialog with a progress bar on it and I use a thread to do the process and to update the progress bar. This worked fine with PyGTK but after converting to PyGObject, I get all the usual improper threading weirdness: the program hangs, but it seems to hang in different parts of the process, etc. So I get the impression that something has changed but I can't figure out what.

Here's this simple PyGTK progressbar example: http://aruiz.typepad.com/siliconisland/2006/04/threads_on_pygt.html As presented on that page, the code works. I've converted it to PyGObject introspection and I get the same problems as in my program: it hangs, it doesn't properly update the progress bar, etc.

import threading
import random, time
from gi.repository import Gtk, Gdk
#Initializing the gtk's thread engine
Gdk.threads_init()


class FractionSetter(threading.Thread):
    """This class sets the fraction of the progressbar"""

    #Thread event, stops the thread if it is set.
    stopthread = threading.Event()

    def run(self):
        """Run method, this is the code that runs while thread is alive."""

        #Importing the progressbar widget from the global scope
        global progressbar 

        #While the stopthread event isn't setted, the thread keeps going on
        while not self.stopthread.isSet() :
            # Acquiring the gtk global mutex
            Gdk.threads_enter()
            #Setting a random value for the fraction
            progressbar.set_fraction(random.random())
            # Releasing the gtk global mutex
            Gdk.threads_leave()

            #Delaying 100ms until the next iteration
            time.sleep(0.1)

    def stop(s