Incorrect encoding of letter's headings

[Vitaly A. Repin]

Hello, All!

When I write the subject of my letter in russian (koi8-r encoding),
the following transformation occurs with letters of the "Subject" field:

Subject: =?koi8-r?B?9MXT1CDS1dPTy8/HzyDawcfPzM/Xy8E=?=

What's the problem?  And how can I solve it?

Thanks & Good-bye!
-- 
WBR & WBW, Vitaly.