Maven Source Properties That Don't Work

When I do 'Maven > Update Project Configuration' in Eclipse, this seems not to work: 

    <properties>

        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

        <project.build.source>1.6</project.build.source>

        <project.build.target>1.6</project.build.target>

    </properties>

    

But this seems to work: 

    <build>

        <plugins>

            <plugin>

                <artifactId>maven-compiler-plugin</artifactId>

                <configuration>

                    <source>1.6</source>

                    <target>1.6</target>

                </configuration>

            </plugin>

     ...

    

Too bad, since the first xml is neater. 

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PS. One sign that there is some mix-up with 1.5/1.6, is that the @Override annotation acts up.