merge issue from parent causing executions to be run multiple times

Has parent/child project

parent
child1

in parent's pom.xml, define a "run"
<build>
<plugins>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<executions>
<execution>
<id>e1</id>
<phase>generate-sources</phase>
<configuration>
<tasks>
<echo message="ant e1" />
</tasks>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>

In child,'s pom.xml, define another "run"
<build>
<plugins>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<executions>
<execution>
<id>e2</id>
<phase>generate-sources</phase>
<configuration>
<tasks>
<echo message="ant e2" />
</tasks>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>

Expect the two declaration to be merged so that during the generate-sources phase for the child I will see
ant e1
ant e2

what happens right now
[INFO] [antrun:run {execution: e1}]
[INFO] Executing tasks
[echo] ant e1
[INFO] Executed tasks
[INFO] [antrun:run {execution: e2}]
[INFO] Executing tasks
[echo] ant e2
[INFO] Executed tasks
[INFO] [antrun:run {execution: e1}]
[INFO] Executing tasks
[echo] ant e1
[INFO] Executed tasks
[INFO] [antrun:run {execution: e2}]
[INFO] Executing tasks
[echo] ant e2

help:effective-pom shows the merged pom at the child with merge but duplicated antrun plugin declaration
...
<plugins>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<executions>
<execution>
<id>e1</id>
<phase>generate-sources</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<tasks>
<echo message="ant e1"></echo>
</tasks>
</configuration>
</execution>
<execution>
<id>e2</id>
<phase>generate-sources</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<tasks>
<echo message="ant e2"></echo>
</tasks>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<executions>
<execution>
<id>e1</id>
<phase>generate-sources</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<tasks>
<echo message="ant e1"></echo>
</tasks>
</configuration>
</execution>
<execution>
<id>e2</id>
<phase>generate-sources</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<tasks>
<echo message="ant e2"></echo>
</tasks>
</configuration>
</execution>
</executions>
</plugin>
..

Attached please find
. *.zip has a sample parent/child example, you can go to child1 and do
mvn compile

. epom.xml is the output of 'mvn help:effective-pom' for the child project