为什么当运行mvn install两次时,来自生成源的类就消失了?

我有一个从xsd模式用jaxb生成java类的项目。

POM包含

        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>jaxb2-maven-plugin</artifactId>
            <version>2.2</version>
            <executions>
                <execution>
                    <id>xjc</id>
                    <goals>
                        <goal>xjc</goal>
                    </goals>
                    <phase>generate-sources</phase>
                </execution>
            </executions>
            <configuration>
                <!-- The package of your generated sources -->
                <packageName>com.melexis.mfgdil.b2mml</packageName>
                <sources>
                    <source>src/main/schema/AllSchemas.xsd</source>
                </sources>
            </configuration>
        </plugin>

当我打字时 mvn clean install Java源代码是从 xsd文件到 目标/生成源/jaxb ,编译并最终 目标/类 ,太好了!

当我敢马上跑 mvn install 再一次,没有任何改变,我明白了:

[INFO] --- jaxb2-maven-plugin:2.2:xjc (xjc) @ b2mml ---
[INFO] Ignored given or default xjbSources 
[/home/pti/Projects/b2mml/src/main/xjb], since it is not an existent file or directory.
[INFO] No changes detected in schema or binding files - skipping JAXB 
generation.  
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ b2mml ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 0 resource
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ b2mml ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /home/pti/Projects/b2mml/target/classes
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ b2mml ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /home/pti/Projects/b2mml/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ 

2亿英镑--- [信息]无需编译-所有类都是最新的 [信息]

这个 目标/类 文件夹被清除,并且 目标/生成源 已经不存在了,在我的 src/main/java文件 树在左边。

我不明白为什么maven会检测到更改,而且我得到的更少的是,它会重新编译模块,但会忘记生成的源代码。我忘了什么?