Gui freezing in supplied example

[peter-langer]

The gui randomly stops working when executing examples/test_bokehgui.grc.

Error message is:
2017-10-27 10:51:27,108 error handling message Message 'PATCH-DOC' (revision 1): KeyError('references',) 2017-10-27 10:51:27,175 Bad header with no msgtype was: {u'references': [], u'events': [{u'new': u'5.82', u'model': {u'type': u'TextInput', u'id': u'06003215-eba3-4186-b43f-5785170b4e23'}, u'kind': u'ModelChanged', u'attr': u'value'}]} 2017-10-27 10:51:27,176 Bokeh Server protocol error: No 'msgtype' in header, closing connection

This happens after a few seconds and only when using the sliders.

It seems this has to do with the function_probe block and the Bokeh Gui Label block. Changing a slider that does not affect the Gui Label does not trigger the crash.