Ok, I have fixed the problem by myself:
In wp-admin\export.php from Line 170:
<description></description>
<excerpt:encoded><![CDATA[<?php echo $post->post_excerpt ?>]]></excerpt:encoded>
<content:encoded><![CDATA[<?php echo $post->post_content ?>]]></content:encoded>
and in wp-admin\import\wordpress.php from Line 228:
$post_author = $this->get_tag( $post, 'dc:creator' );
$post_excerpt = $this->get_tag( $post, 'excerpt:encoded' );
$post_excerpt = str_replace(array ('<![CDATA[', ']]>'), '', $post_excerpt);
$post_excerpt = preg_replace('|<(/?[A-Z]+)|e', "'<' . strtolower('$1')", $post_excerpt);
$post_excerpt = str_replace('<br>', '<br />', $post_excerpt);
$post_excerpt = str_replace('<hr>', '<hr />', $post_excerpt);
$post_content = $this->get_tag( $post, 'content:encoded' );
Works perfect for me.
Helli