In the fivestar_form() function, there is a call to set
$settings['text'] => variable_get('fivestar_text_' . $node->type, 'combo')
I believe that string 'combo' should instead be 'dual', based upon the values that are defined for the "Text display style" found in fivestar_form_alter(). There is one other instance similar to this in fivestar_views_widget_hander(), but I'm not as confident in my assessment there since I haven't really been looking at that code.