Subject field corruption

[NOwlar]

I use Postfix 2.0.10 with TLS patch, cyrus-imapd 2.1.13, sasl 2.1.13
The problem is as follow:
When a message with russian charset characters (KOI8-R, WIN1251) in Subject
field arrives or is moved into the Sent Items folders by Outlook Express,
each russian character is replaced by an X (ex: Re: XXXX XXXX mazda 626
XXXX). I happens only when the Subject field is without charaterset
specification.

I dumped mailboxes with cyrdump, the Xes are in.

What can be wrog?

I will appreciate any help.
Max.

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Real programmers never sleep. They enter brainsaver mode.