External Web Resources are not properly filtered

• Testcase included:

  yes

I have configured an external web resource location in the project's web module
..
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<webResources>
<resource>
<directory>${basedir}/src/main/webresources</directory>
<filtering>true</filtering>
</resource>
</webResources>
</configuration>
</plugin>

I need to apply a filter to jetty-env.xml
...
<Arg>
<New class="oracle.jdbc.pool.OracleConnectionPoolDataSource">
<Set name="URL">${jdbc.url}</Set>
<Set name="user">${jdbc.user}</Set>
<Set name="password">${jdbc.password}</Set>
</New>
</Arg>
...

Parent POM contains properties like these:
...
<properties>
<jdbc.url>jdbc:oracle:thin:@localhost:1521:orcl</jdbc.url>
<website.url>scp://www.yourcompany.com/www/docs/project</website.url>
...

The result aftre filtering is following:
..
<Arg>
<New class="oracle.jdbc.pool.OracleConnectionPoolDataSource">
<Set name="URL">http://maven.apache.org</Set>
...

I have enclosed example project.