Buildnumber plugin doesn't fail on doCheck if file is modified

I use the following configuration in my pom.xml:

<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>buildnumber-maven-plugin</artifactId>
<version>1.0-beta-4</version>
<executions>
<execution>
<phase>verify</phase>
<goals>
<goal>create</goal>
</goals>
</execution>
</executions>
<configuration>
<doCheck>true</doCheck>
<doUpdate>false</doUpdate>
</configuration>
</plugin>
</plugins>

Steps to reproduce:
1. Check out the project.
2. Modify a .java file that is under version control, e.g. add a method to my-package\MyClass.java. The file gets the dirty icon in Eclipse.
3. Run "mvn -U buildnumber:create". The build succeeds, but it should fail.

Interestingly, the log says:
[DEBUG] M src\main\java\mypackage\MyClass.java

So, the SVN client correctly identified the modified file, but the buildnumber plugin didn't react on this result.

If I delete my-package\MyClass.java, it works as expected:
[ERROR] Failed to execute goal org.codehaus.mojo:buildnumber-maven-plugin:1.0-beta-4:create (default-cli) on project trial-maven: Cannot create the build number because you have local modifications :
[ERROR] [ src\main\java\my-package\MyClass.java:deleted]