[mew-int 2993] how to post a mew attachment with chinese file name.

hi mew developer:
   i have used mew for about one year,when i use mew version 6.5beta under
windows.i could not send out new mail when its attchment name has chinese
characters,so i redefine following functions like this:
=============================================
  (defun mew-ecsdb-guess-string (str)
  '((ascii chinese-gb2312) cn-gb-2312 "base64" "B" t))
=============================================
this is working,mail.google.com and mew could recognize my email without
 problem.but outlook could not recognize it.
i found that mew mail header lacks the line "Content-Language: zh-cn", and
its multiple part is like this:
=============================================
Content-Type: Application/Msword;
 name*=gb2312''%3D%3Fgb2312%3FB%3Fz%2B7Ev9bcsahf0O2%2BtMzOXzIwMTEwNDI5LmRvYw%3D%3D%3F%3D
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename*=gb2312''%CF%EE%C4%BF%D6%DC%B1%A8%5F%D0%ED%BE%B4%CC%CE%5F20110429%2Edoc
=============================================

but outlook's same region is like this:
=============================================
Content-Type: application/msword;
name="=?gb2312?B?z+7Ev9bcsahfwfWx+F8yMDExMDUwNi5kb2M=?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="=?gb2312?B?z+7Ev9bcsahfwfWx+F8yMDExMDUwNi5kb2M=?="
=============================================

could you give me some advise or this is the mew's one bug?

With best regards.
jingtao
2011.5.11