UTF-8 chars not shown from Outlook 15

I have RT where attachments are exported to disk from database.

While browsing ticket history, I see broken UTF-8 symbols in messages send by mail. If I open the same message using With Headers or Without headers* in separate window, the UTF-8 chars are displayed correctly.

Message has following headers:

content-type: text/html; charset="utf-8"
X-RT-Original-Encoding: utf-8
Content-Transfer-Encoding: base64
Content-Length: 17357

<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">

Where is the problem?