ERROR:tryton.common.common:  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/view/list.py", line 1003, in __sig_switch
    if not self.screen.row_activate() and self.children_field:

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/screen/screen.py", line 340, in default_row_activate
    self.switch_view(view_type='form')

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/screen/screen.py", line 375, in switch_view
    self.display()

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/screen/screen.py", line 729, in display
    view.display()

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/view/form.py", line 469, in display
    widget.display(record, field)

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/view/form_gtk/reference.py", line 135, in display
    super(Reference, self).display(record, field)

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/view/form_gtk/many2one.py", line 294, in display
    self.set_text(field.get_client(record))

  File "/usr/local/lib/python2.7/dist-packages/tryton-3.4.6-py2.7.egg/tryton/gui/window/view_form/view/form_gtk/reference.py", line 124, in set_text
    self.widget_combo.handler_block_by_func(self.sig_changed_combo)

nothing connected to <bound method Reference.sig_changed_combo of <tryton.gui.window.view_form.view.form_gtk.reference.Reference object at 0x7fead5d51050>>