OK, I have found the problem.
I use some reporting plugins. In the documentation of the failsafe-maven-plugin
I found, that the <encoding>
configuration – of course – uses ${project.reporting.outputEncoding}
by default.
So I added the property as a child element of the project
element and everything is fine now:
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
</properties>
See also http://maven.apache.org/general.html#encoding-warning