The hibernate4-maven-plugin computes MD5-sums for all found annotated classes and stores them together with the generated schema. If no classes were changed or added and the dialect wasn't changed too, it automatically skips the configured schema-export, to speed up the development cycle.

The plugin signals, that the execution was skipped by setting the maven property $\{hibernate.export.skipped\} to true. This may be helpful, because other plugins like dbunit-plugin may fail, when the execution is skipped.

If you need the hibernate4-maven-plugin to <never skip execution automatically>, you can force it to do so, if you set the parameter force to true:

<plugin>
  <groupId>de.juplo</groupId>
  <artifactId>hibernate4-maven-plugin</artifactId>
  <version>1.0.5</version>
  <configuration>
    <force>true</force>
  </configuration>
</plugin>

Or you may specify -Dhibernate.export.force=true at the command line, if you want to force hibernate4-maven-plugin only once.