Finishing session and starting a new one crashes

Steps to reproduce:
1) start normal testing session
2) finish it normally
3) hit 'X' action in the header on results screen
4) start a new session
5) select test plan

BOOM:
Traceback (most recent call last):
  File "/home/kissiel/checkbox/checkbox-touch/py/checkbox_touch.py", line 96, in wrapper
    result = func(*args, **kwargs)
  File "/home/kissiel/checkbox/checkbox-touch/py/checkbox_touch.py", line 245, in remember_testplan
    self.assistant.finalize_session()
  File "/home/kissiel/checkbox/plainbox/plainbox/impl/decorators.py", line 104, in wrapper
    raise exc
  File "/home/kissiel/checkbox/plainbox/plainbox/impl/decorators.py", line 98, in wrapper
    return func(*args, **kwargs)
  File "/home/kissiel/checkbox/plainbox/plainbox/impl/session/assistant.py", line 1077, in finalize_session
    UsageExpectation.of(self).enforce()
  File "/home/kissiel/checkbox/plainbox/plainbox/impl/developer.py", line 222, in enforce
    raise UnexpectedMethodCall(self.cls, fn_name, allowed_pairs)
plainbox.impl.developer.UnexpectedMethodCall:
Uh, oh...