title: Maven build-helper plugin not including sources in multi module project
body: <p>I am generating webservice artifacts with cxf-xjc and attempting to add them to source with the build-helper plugin. This was working properly when it was used in a single Maven project, but now that I've moved into a multi-module project, the generated classes are not being included as source. </p>
  
  <p>The classes are generated properly and the build-helper plugin is executing after the classes are generated. The output for build-helper shows the correct source directory path where the classes are located and shows 'added'. </p>
  
  <p><strong><em>pom.xml</em></strong></p>
  
  <pre><code>&lt;!-- CXF --&gt;
  &lt;plugin&gt;
      &lt;groupId&gt;org.apache.cxf&lt;/groupId&gt;
      &lt;artifactId&gt;cxf-xjc-plugin&lt;/artifactId&gt;
      &lt;version&gt;2.3.0&lt;/version&gt;
      &lt;executions&gt;
          &lt;execution&gt;
              &lt;id&gt;generate-xsd-sources&lt;/id&gt;
              &lt;phase&gt;generate-sources&lt;/phase&gt;
              &lt;goals&gt;
                  &lt;goal&gt;xsdtojava&lt;/goal&gt;
              &lt;/goals&gt;
              &lt;configuration&gt;
                  &lt;sourceRoot&gt;${basedir}/target/generated-sources/java&lt;/sourceRoot&gt;
                  &lt;xsdOptions&gt;
                      &lt;xsdOption&gt;
                          &lt;!-- &lt;bindingFile&gt;src/main/resources/request.xjb&lt;/bindingFile&gt; --&gt;
                          &lt;xsd&gt;src/main/resources/request.xsd&lt;/xsd&gt;
                          &lt;packagename&gt;${services.package}.package.request&lt;/packagename&gt;
                      &lt;/xsdOption&gt;
                      &lt;xsdOption&gt;
                          &lt;!-- &lt;bindingFile&gt;src/main/resources/response.xjb&lt;/bindingFile&gt; --&gt;
                          &lt;xsd&gt;src/main/resources/response.xsd&lt;/xsd&gt;
                          &lt;packagename&gt;${services.package}.package.response&lt;/packagename&gt;
                      &lt;/xsdOption&gt;
                  &lt;/xsdOptions&gt;
              &lt;/configuration&gt;
          &lt;/execution&gt;
      &lt;/executions&gt;
  &lt;/plugin&gt;
  
  &lt;!-- Move generated to source --&gt;
  &lt;plugin&gt;
      &lt;groupId&gt;org.codehaus.mojo&lt;/groupId&gt;
      &lt;artifactId&gt;build-helper-maven-plugin&lt;/artifactId&gt;
      &lt;executions&gt;
          &lt;execution&gt;
              &lt;id&gt;add-source&lt;/id&gt;
              &lt;phase&gt;generate-sources&lt;/phase&gt;
              &lt;goals&gt;
                  &lt;goal&gt;add-source&lt;/goal&gt;
              &lt;/goals&gt;
              &lt;configuration&gt;
                  &lt;sources&gt;
                      &lt;source&gt;${project.build.directory}/generated-sources/java&lt;/source&gt;
                  &lt;/sources&gt;
              &lt;/configuration&gt;
          &lt;/execution&gt;
      &lt;/executions&gt;
  &lt;/plugin&gt;
  </code></pre>
  
  <p><strong>Console snip</strong></p>
  
  <pre><code>[INFO] --- **cxf-xjc-plugin:2.3.0:xsdtojava (generate-xsd-sources) @ aggregation-jaxrs-api** ---
  [INFO] 
  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ aggregation-jaxrs-api ---
  [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
  [INFO] Copying 2 resources
  [INFO] 
  [INFO] --- maven-compiler-plugin:2.0.2:compile (default-compile) @ aggregation-jaxrs-api ---
  [INFO] Compiling 55 source files to C:\workspace\aggregation-parent\aggregation-jaxrs-api\target\classes
  [INFO] 
  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ aggregation-jaxrs-api ---
  [WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
  [INFO] Copying 0 resource
  [INFO] 
  [INFO] --- maven-compiler-plugin:2.0.2:testCompile (default-testCompile) @ aggregation-jaxrs-api ---
  [INFO] Nothing to compile - all classes are up to date
  [INFO] 
  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ aggregation-jaxrs-api ---
  [INFO] 
  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ aggregation-jaxrs-api ---
  [INFO] Building jar: C:\workspace\aggregation-parent\aggregation-jaxrs-api\target\aggregation-jaxrs-api-1.0-SNAPSHOT.jar
  [INFO] 
  **[INFO] --- build-helper-maven-plugin:1.12:add-source (add-source) @ aggregation-jaxrs-api ---
  [INFO] Source directory: C:\workspace\aggregation-parent\aggregation-jaxrs-api\target\generated-sources\java added.**
  </code></pre>
  
  <p>This configuration worked fine prior to me moving it to a module. I've changed to build-helper phase between generate-sources and process-sources phase with no luck. I am using Spring Tool Suite 3.8 which is based on Eclipse Neon 4.6.1.</p>
  
  <p>Thanks</p>