Zend_Form_Element_File - 表单错误时文件丢失

I'm creating a Zend Form which includes a Zend Form Element File to allow the user to upload a file. When there is an error on the form (i.e. validation fails), when it is re-displayed for the user to correct, the file upload box is empty (so they have to click browse and select it again).I'm creating a Zend Form which includes a Zend