mail fails to decode encoded addresses

mail_decode_fail

>> puts m.to_s                                                             
Date: Thu, 21 Oct 2010 16:28:20 +0100
From: craig mcmillan <victorianexercises@gmail.com>
To: =?UTF-8?B?ImNyYWlnIOaXpeacrOWbvSI=?= <craig@trampolinesystems.com>
Message-ID: <4CC05C14.6030501@mccraig.net>
Subject: =?UTF-8?Q?big_in_=E6=97=A5=E6=9C=AC=E5=9B=BD?=
Mime-Version: 1.0
Content-Type: text/plain;
 charset=UTF-8;
 format=flowed
Content-Transfer-Encoding: base64
User-Agent: Postbox 2.0.1 (Macintosh/20101011)

VW5pY29kZSBib2R5IGlzIGJpZyBpbiDml6XmnKzlm70=
=> nil
>> m.subject                                                               
=> "big in 日本国"
>> m.body.to_s                                                             
=> "Unicode body is big in 日本国"
>> m[:to].tree.addresses.first.name                                        
=> "=?UTF-8?B?ImNyYWlnIOaXpeacrOWbvSI=?="
>> Mail::Encodings.decode_encode(m[:to].tree.addresses.first.name, :decode)
=> ""craig 日本国""