mfw_managed_file_value uses #parents instead of #array_parents

function mfw_managed_file_values uses '#parents' to get the file element from the form array, however this is not correct drupal code. #parents is for locating values in the $form_state['values'] array #array_parents is for locating elements in the form array. This means that the widget does not work on any form where '#parents' and '#array_parents' do not match.