Why at sending on SOAP the letter in ISO-8859-5 ?

GW8.0.2HP3.
WS(send in UTF-8)-->SOAP---->POA-->MTA--->GWIA---->INTERNET(send in ISO-8859-5)
Why at sending on SOAP the letter in an Internet leaves in ISO-8859-5 ?
In the WS compose new mail in UTF-8 and send over SOAP to the foreign internet user (send from Evolution).
When foreign internet user receive mail - in the receieved mail:
.....
Subject: =?ISO-8859-5?B?3+De0dA=?=
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-5
Content-Transfer-Encoding: binary
Content-Disposition: inline
....

Why ine the ISO-8859-5 ??

When send from the GW8.0.2hp3 client - All OK. oreign user received mail in the UTF-8.

Help me, please !

Serg