src/main/java/org/codehaus/plexus/archiver/jar/JarArchiver.java
protected void cleanUp()
        throws IOException
    {
        super.cleanUp();

        // we want to save this info if we are going to make another pass
        if ( !doubleFilePass || !skipWriting )
        {
            manifest = null;
            configuredManifest = savedConfiguredManifest;
            filesetManifest = null;
            originalManifest = null;
        }
        rootEntries.removeAllElements();
    }
protected void cleanUp()
        throws IOException
    {
        super.cleanUp();

        // we want to save this info if we are going to make another pass
        if ( !doubleFilePass || !skipWriting )
        {
            manifest = null;
            configuredManifest = savedConfiguredManifest;
            filesetManifest = null;
            originalManifest = null;
        }
        rootEntries.removeAllElements();
    }
Make sure we don't think we already have a MANIFEST next time this task
gets executed.

@see ZipArchiver#cleanUp