${parentProject}\ in default site descriptor doesn't resolve

When building a site I get a xml parser error because ${parentProject} is not substituted with the right value. If I remove it from the site plugin default site descriptor it runs fine.

[INFO] ----------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ----------------------------------------------------------------------------
[INFO] Error parsing site descriptor

Embedded error: expected START_TAG or END_TAG not TEXT (position: TEXT seen ...OJECT_URL_SET"/>\r\n </links>\r\n ${parentProject}\r\n \r\n <m... @12:7)