martifact won't inherit project.build.outputTimestamp

[Delany]

Hi. Why does maven-artifact-plugin complain

  [WARNING] project.build.outputTimestamp property should not be inherited
but defined in parent POM from reactor

I never had a plugin complain about utilizing inheritance. Why does it care?
When I add the line to the project the warning disappears


<project.build.outputTimestamp>${maven.build.timestamp}</project.build.outputTimestamp>

Thanks,
Delany