Variables not expanded in Maven plugin

In my maven plugin I have the following:

<dependencySets>
    <dependencySet>
            <scope>runtime</scope>
            <outputDirectory>/dir/${project.parent.artifactId}-${project.version}/${project.artifactId}/lib</outputDirectory>
    </dependencySet>
</dependencySets>

When mvn clean package开发者_如何学运维 is run, the outputDirectory is literally dir/${project.parent.artifactId}-${project.version}/... That is, the variables aren't being expanded. I am not getting any kind of variable not found message (nor should I). What could cause variables not to be expanded?

---

Can you check if the following works? Essentially, removing the project prefix from the variable names, since maven2 is not strict about this.

<outputDirectory>/dir/${parent.artifactId}-${version}/${artifactId}/lib</outputDirectory>

You may also want to check if you are using the last maven assembly plugin