Cannot find dependency in Ant plugin based on multiple build scripts

I am trying to create a custom ant plugin for Maven, based on multiple build scripts. There is a note in the documentation about it: http://maven.apache.org/guides/plugin/guide-ant-plugin-development.html (see "A Note on Multiple Build Scripts"), but I have not been able to make it work.

Here are the scripts:

<root>\src\main\scripts\A.build.xml
-----------------------------------
<project>
<import file="C.build.xml"/>
<target name="hello" depends="dependency">
<echo>Hello, World</echo>
</target>
</project>

<root>\src\main\scripts\A.mojos.xml
-----------------------------------
<pluginMetadata>
<mojos>
<mojo>
<goal>hello</goal>
<call>hello</call>
</mojo>
</mojos>
</pluginMetadata>

<root>\src\main\scripts\B.build.xml
-----------------------------------
<project>
<target name="hello">
<echo>Hello, World</echo>
</target>
</project>

<root>\src\main\scripts\B.mojos.xml
-----------------------------------
<pluginMetadata>
<mojos>
<mojo>
<goal>hello2</goal>
<call>hello</call>
</mojo>
</mojos>
</pluginMetadata>

<root>\src\main\scripts\C.build.xml
-----------------------------------
<project>
<target name="dependency">
<echo>This is the dependency</echo>
</target>
</project>

<root>\pom.xml
--------------
<project>
<modelVersion>4.0.0</modelVersion>

<groupId>org.myproject.plugins</groupId>
<artifactId>hello-plugin</artifactId>
<version>1.0-SNAPSHOT</version>

<packaging>maven-plugin</packaging>

<name>Hello Plugin</name>

<dependencies>
<dependency>
<groupId>org.apache.maven</groupId>
<artifactId>maven-script-ant</artifactId>
<version>2.2.1</version>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<artifactId>maven-plugin-plugin</artifactId>
<version>2.9</version>

<dependencies>
<dependency>
<groupId>org.apache.maven.plugin-tools</groupId>
<artifactId>maven-plugin-tools-ant</artifactId>
<version>2.9</version>
</dependency>
</dependencies>

<configuration>
<goalPrefix>hello</goalPrefix>
</configuration>
</plugin>
</plugins>
</build>
</project>

At the root level, I run "mvn clean install", which is successful.

Then I run "mvn org.myproject.plugins:hello-plugin:hello2", which is also successful and produces the "Hello, World" output.

However, when running "mvn org.myproject.plugins:hello-plugin:hello", I get this:

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building Hello Plugin 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] — hello-plugin:1.0-SNAPSHOT:hello (default-cli) @ hello-plugin —
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.531s
[INFO] Finished at: Thu Mar 08 12:52:25 PST 2012
[INFO] Final Memory: 3M/15M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.myproject.plugins:hello-plugin:1.0-SNAPSHOT:hello (default-cli) on project hello-plugin: Failed to execute: Executing Ant script: A.build.xml [hello]: Failed to parse. Cannot find C.build.xml imported from C:\DOCUME~1\joanes\LOCALS~1\Temp\plexus-ant-component9129296102162378706.build.xml -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

By looking at the error, the script is executed in a temporary folder, hence it cannot find the imported C.build.xml.