Macro in url of parent project is not expanded if only the site for a subproject is built

The parent POM has:

<url>${gxSite}/${project.build.finalName}</url>

where "gxSite" is defined in settings.xml as "http://dna.dupont.com/site"

The module POM has:

<parent>
		<relativePath>../MavenRoot/pom.xml</relativePath>
		<groupId>genomix</groupId>
		<artifactId>LeadTracker</artifactId>
		<version>0.1</version>
	</parent>
...

	<url>${project.artifactId}</url>

and the "site.xml" in the module includes a menu with ref="parent".

If goals "site site:deploy" is run from the parent, the link back to the parent is fine, but if the same goal is run from the module, the link back to the parent is generated as follows:

http://dna.dupont.com/site/LeadTracker-0.1/${gxSite}/LeadTracker-0.1/index.html