Object not found with name 'QQuickItem' and properties {'id': 2}

When running the ubuntu-system-tests test suite, we see this error repeatedly in tests that use the keyboard - they might work once or twice but then will start failing like this:

Traceback (most recent call last):
  File "/tmp/adt-run.ftoeU5/build.pdr/real-tree/ubuntu_system_tests/tests/test_with_webbrowser.py", line 193, in test_create_bookmark_and_navigate
    self.browser.go_to_url(test_data.get('ubuntu').entered_url)
  File "/tmp/adt-run.ftoeU5/build.pdr/real-tree/ubuntu_system_tests/helpers/webbrowser.py", line 64, in go_to_url
    self.address_bar.write(url)
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/webbrowser_app/emulators/browser.py", line 255, in write
    self.text_field.write(text, clear)
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/autopilot/logging.py", line 46, in inner
    return f(instance, *args, **kwargs)
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/ubuntuuitoolkit/_custom_proxy_objects/_textfield.py", line 49, in write
    self.keyboard.type(text)
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/autopilot/input/_osk.py", line 105, in type
    self._keyboard.type(string, delay)
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/ubuntu_keyboard/emulators/keyboard.py", line 211, in type
    self.press_key(char)
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/ubuntu_keyboard/emulators/keyboard.py", line 164, in press_key
    if not self.is_available():
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/ubuntu_keyboard/emulators/keyboard.py", line 137, in is_available
    return (self.keyboard.state == "SHOWN")
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/autopilot/introspection/dbus.py", line 411, in __getattr__
    self.refresh_state()
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/autopilot/introspection/dbus.py", line 367, in refresh_state
    _, new_state = self._get_new_state()
  File "/tmp/adt-run.ftoeU5/deps/usr/lib/python3/dist-packages/autopilot/introspection/dbus.py", line 429, in _get_new_state
    raise StateNotFoundError(self.__class__.__name__, id=self.id)
autopilot.exceptions.StateNotFoundError: Object not found with name 'QQuickItem' and properties {'id': 2}.

A good way to reproduce this is to branch lp:ubuntu-system-tests and run it with the webbrowser tests:

./run-system-tests ubuntu_system_tests.tests.test_with_webbrowser

As mentioned, the first couple of tests might pass but once it starts failing it will continue failing.

Note that the tests restart unity between each test so this might be something to investigate.

$ system-image-cli -i
current build number: 85
device name: krillin
channel: ubuntu-touch/rc-proposed/bq-aquaris.en
last update: 2015-08-05 07:23:21
version version: 85
version ubuntu: 20150805
version device: 20150716-fb60d96
version custom: 20150717-820-30-25-vivid