only in patch2:
unchanged:
--- a/modules/field/modules/options/options.module
+++ b/modules/field/modules/options/options.module
@@ -104,10 +104,15 @@ function options_field_widget_form(&$form, &$form_state, $field, $instance, $lan
       }
       $element += array(
         '#type' => $multiple ? 'checkboxes' : 'radios',
-        // Radio buttons need a scalar value.
-        '#default_value' => $multiple ? $default_value : reset($default_value),
         '#options' => $options,
       );
+      // Only set a default value if one has been supplied.
+      if (count($default_value)) {
+        $element += array(
+          // Radio buttons need a scalar value.
+          '#default_value' => $multiple ? $default_value : reset($default_value);
+        );
+      }
       break;
 
     case 'onoff':