get_children_by_type() crashes

I am evaluating autopilot for GTK programs (so this might be an autopilot-gtk bug). I have this simple test:

$ cat autopilot_tests/test_evince.py
from autopilot.testcase import AutopilotTestCase
from autopilot.introspection.gtk import GtkIntrospectionTestMixin

class Evince(AutopilotTestCase, GtkIntrospectionTestMixin):
    def setUp(self):
        super(Evince, self).setUp()
        self.application = self.launch_test_application('evince')

    def test_children(self):
        print '---- children ----'
        print self.application.get_children()
        print '---- child 0 ----'
        print dir(self.application.get_children()[0])

        # crashes:
        print '---- EvWindow children ----'
        print self.application.get_children_by_type('EvWindow')
-------------------------- 8< -----------------------

The last line causes the Evince window to crash/hang; I get two metric tons of

** (evince:27302): WARNING **: unsupported type: GtkContainer

for every Gtk data type, and at the end

Traceback (most recent call last):
  File "/home/martin/ubuntu/tmp/autopilot_tests/test_evince.py", line 20, in test_open
    print self.application.get_children_by_type('EvWindow')
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/dbus.py", line 210, in get_children_by_type
    instances = self.get_children()
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/dbus.py", line 240, in get_children
    state_dicts = self.get_state_by_path(query)
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/dbus.py", line 299, in get_state_by_path
    ).GetState(piece)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
DBusException: org.freedesktop.DBus.Error.NoReply: Message did not receive a reply (timeout by message bus)

(complete output is in attachment).

However, this seems to work:

        print self.application.select_single('EvWindow')