Notice views_handler_field->advanced_render()

Dear all,

Thank you for this wonderfull module, it's one or the most amazing thing in Drupal.

Recently I started to get this notice:
Notice: Undefined property: view::$row_index in views_handler_field->advanced_render() (line 1149 of /home/.../public_html/sites/all/modules/views/handlers/views_handler_field.inc).

What could this be?