utf8 encoding for solr not working

[Merlin Morgenstern]

I am running solr 3.5 with a mysql data connector. Solr is configured to
use UTF8 as encoding:

<dataConfig>
<dataSource type="JdbcDataSource"
            driver="com.mysql.jdbc.Driver"
            url="jdbc:mysql://localhost/test"
            user="solr"
            password="tester"
            convertType="true"
            batchSize="-1"
            encoding="UTF-8" />

unfortunatelly solr does encode special characters like "ä" into
htmlentities:

&auml;

which leads to problems when cutting strings with php mb_substr(..)

How can I configure solr to deliver UTF-8 instead of htmlentities?

Thank you for any help.