maven-dependency-plugin ignores -Dmaven.local.repo setting

If a maven build is launched with a custom local repo defined, the local repo is not inherited/understood by the dependency plugin.

Ex:
mvn -Dmaven.local.repo=c:\temp\repo clean package -X

I see the following in the debug output
[DEBUG] Configuring mojo 'org.apache.maven.plugins:maven-dependency-plugin:2.10:copy' with basic configurator -->
[DEBUG] (s) groupId = ca.tbt
[DEBUG] (s) artifactId = tbt-applet
[DEBUG] (s) version = 2.0.1-SNAPSHOT
[DEBUG] (s) groupId = ca.tbt
[DEBUG] (s) artifactId = tbt-val-applet
[DEBUG] (s) version = 2.0.1-SNAPSHOT
[DEBUG] (s) artifactItems = [ca.tbt:tbt-applet:2.0.1-SNAPSHOT:jar, ca.tbt:tbt-val-applet:2.0.1-SNAPSHOT:jar]
[DEBUG] (s) local = id: local
url: file:///C:/Users/C45841A6/.m2/repository/
layout: default
snapshots: [enabled => true, update => always]
releases: [enabled => true, update => always]

As you can see, the local repo is pointing to the default ~/.m2/repository repo.

Consequently, any artifacts generated in my custom local repo are not available to the plugin and the build fails.

Defining -DlocalRepositoryDirectory has no impact