MIME encoding problem

[osakana]

I tried to send e-mail by ISO-2022-JP encoding from roundcube svn 404.
"Subject" is encoded ISO-2022-JP.
But, "From" and "To" are not encoded.

The following are the comparisons of the header.

=== RoundCube SVN401,404 ===
From: 実験メールです <username@domain>
To: 実験メールです <username@domain>
Subject: =?ISO-2022-JP?Q?=1B=24B=3CB=38=33=25a!=3C=25k=24G=24=39=1B=28 B?=

=== RoundCube SVN396 ===
From: =?ISO-2022-JP?Q?=E5=AE=9F=E9=A8=93=E3=83=A1=E3=83=BC=E3=83=AB =E3=81=A7=E3=81=99?= <username@domain>
To: 実験メールです <username@domain>
Subject: =?ISO-2022-JP?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?=

=== hotmail ===
From: =?iso-2022-jp?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?= <username@domain>
To: =?iso-2022-jp?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?= <username@domain>
Subject: =?iso-2022-jp?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?=

=== Becky, one of Japanese mail software (http://www.rimarts.co.jp)===
From: =?ISO-2022-JP?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?= <username@domain>
To: =?ISO-2022-JP?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?= <username@domain>
Subject: =?ISO-2022-JP?B?GyRCPEI4MyVhITwlayRHJDkbKEI=?=

=== Ximian Evolution 1.4.6.335 (Solaris10) ===
Subject: =?iso-2022-jp?B?GyRCPEI4MyVhITwlayRHJDkbKEo=?=
From: =?iso-2022-jp?B?GyRCPEI4MyVhITwlayRHJDkbKEo=?= <username@domain>
To: =?iso-2022-jp?B?GyRCPEI4MyVhITwlayRHJDkbKEo=?= <username@domain>