maybe it is a mail funtion bug

I am using wordpress 2.1.2. My site is http://www.juyimeng.com.
Because my site using chinese character,the mail content is chinese in utf8 encoding.
I found the system email’s subject is in wrong encoding, the subject can’t be read, but the content is absolutely normal.
After added one line in the wp_mail function (wp-includes/pluggable.php), the subject’s character can be read.
The solution is add
$subject = “=?”.get_option(‘blog_charset’).”?B?”.base64_encode($subject).”?=”;
before
return @mail($to, $subject, $message, $headers);

this function locate in about line 158.

is it a bug?