Jacoco maven plugin prepare-agent goal getting added twice - maven-3

Question

Tools :
Maven 3.2
Maven Jacoco Plugin - version 0.5.5.201112152213
Issue :
Below is the jacoco pugin included in pom.xml
<build>
<plugins>
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>0.5.5.201112152213</version>
<configuration>
<destFile>${basedir}/target/reports/jacoco.exec</destFile>
<dataFile>${basedir}/target/reports/jacoco.exec</dataFile>
</configuration>
<executions>
<execution>
<id>jacoco-initialize</id>
<goals>
<goal>prepare-agent</goal>
</goals>
</execution>
<execution>
<id>jacoco-site</id>
<phase>package</phase>
<goals>
<goal>report</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
After running effective-pom , I am getting below output -
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>0.5.5.201112152213</version>
<executions>
<execution>
<id>agent</id>
<goals>
<goal>prepare-agent</goal>
</goals>
<configuration>
<destFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</destFile>
<dataFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</dataFile>
<append>true</append>
</configuration>
</execution>
<execution>
<id>jacoco-initialize</id>
<goals>
<goal>prepare-agent</goal>
</goals>
<configuration>
<destFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</destFile>
<dataFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</dataFile>
<append>true</append>
</configuration>
</execution>
<execution>
<id>jacoco-site</id>
<phase>package</phase>
<goals>
<goal>report</goal>
</goals>
<configuration>
<destFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</destFile>
<dataFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</dataFile>
<append>true</append>
</configuration>
</execution>
</executions>
<configuration>
<destFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</destFile>
<dataFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</dataFile>
<append>true</append>
</configuration>
</plugin>
It seems that prepare-agent goal has been included twice . The redundant goal is
<id>agent</id> which is not present in pom.xml file and haven't been added.
So , my question is : why is this goal getting included in pom even though the goal is already configured explicitly with id <id>jacoco-initialize</id>.
EDIT :
Further digging deep into problem , I removed the plugin (jacoco-maven-plugin) altogether from child module and when I run mvn help:effective-pom , interestingly it is still showing jacoco-maven-plugin with only one goal in it as below . It is the same one which gets added additionally. That means parent module is adding this plugin . But there is no reference of this plugin in parent module
<execution>
<id>agent</id>
<goals>
<goal>prepare-agent</goal>
</goals>
<configuration>
<destFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</destFile>
<dataFile>C:\JDeveloper\mywork\myAppTest/target/coverage-reports/jacoco-unit.exec</dataFile>
<append>true</append>
</configuration>
</execution>