cayenne-maven-plugin and its executions environment

Hey,
after spending quite some time, I still can't get the cayenne-maven-plugin (4.4.M2) running as described in the latest "Cayenne-Guide".
The problem is related to the execution environment.
This setting works just fine:

<plugin>
	<groupId>org.apache.cayenne.plugins</groupId>
	<artifactId>cayenne-maven-plugin</artifactId>
	<version>${cayenne.version}</version>
	<configuration>
		<map>${project.basedir}/src/main/resources/scenario/my.map.xml</map>
	</configuration>
	<executions>
		<execution>
			<goals>
				<goal>cgen</goal>
			</goals>
		</execution>
	</executions>
</plugin>

But if I put the configuration inside the execution tag (as described in the Cayenne Guide), Maven can't find the map property.

<plugin>
	<groupId>org.apache.cayenne.plugins</groupId>
	<artifactId>cayenne-maven-plugin</artifactId>
	<version>${cayenne.version}</version>
	<executions>
		<execution>
			<id>execution1</id>
			<configuration>
				<map>${project.basedir}/src/main/resources/my.map.xml</map>
			</configuration>
			<goals>
				<goal>cgen</goal>
			</goals>
		</execution>
	</executions>
</plugin>

This is the error message:
"Failed to execute goal org.apache.cayenne.plugins:cayenne-maven-plugin:4.2.M2:cgen (default-cli) on project my-cayenne: The parameters 'map' for goal org.apache.cayenne.plugins:cayenne-maven-plugin:4.2.M2:cgen are missing or invalid"

According to Stackoverflow, Maven handles the config-tag like this:
1. If the <configuration> is outside the <executions> , it is the configuration for the plugin to be used no matter what the life-cycle phase is.
2. If the <configuration> is inside the <executions>, it is the configuration to be used in certain life-cycle phase.

What could be the reason for this strange behavior?

Kind regards