Coming from @yched's comment in #1875992-56: Add EntityFormDisplay objects for entity forms:
FieldOverview::buildForm()
- '#title' => t($widget_types[$instance['widget']['type']]['label']),
+ '#title' => t($widget_types[$widget_configuration['type']]['label']),
Ouch. Care to open an issue to remove that t() ? (there's another one for the $field['type'] 3 lines above)