PersistenceStateComponent: XML has duplicate lines

This is a crosspost of http://stackoverflow.com/questions/15723824/intellij-idea-plugin-persistence-state-xml-has-duplicate-lines


I have the following Component:

    @State(
        name = "SessionConfiguration",
        storages = {
            @Storage(id = "default", file = StoragePathMacros.PROJECT_FILE),
            @Storage(id = "dir", file = StoragePathMacros.PROJECT_CONFIG_DIR + "/tabsession.xml", scheme = StorageScheme.DIRECTORY_BASED)
        }
    )
    public class SessionComponent implements ProjectComponent, PersistentStateComponent<Element> {

    ...

        @Nullable
        @Override
        public Element getState() {
            LOG.debug("Saving state");

            final Element element = new Element("tabsession");

            // meta configuration information
            final Element stateElement = new Element("state");
            stateElement.setAttribute("version", Integer.toString(STATE_VERSION));
            element.addContent(stateElement);

            // session data
            final Element sessionsElement = new Element("sessions");
            for(SessionState.Session session : sessionState.sessions) {
                final Element sessionElement = new Element("session");
                sessionElement.setAttribute("name", session.name);
                final Element filesElement = new Element("files");
                for(String path : session.files) {
                    final Element fileElement = new Element("file");
                    fileElement.setAttribute("path", path);
                    filesElement.addContent(fileElement);
                }
                filesElement.setAttribute("focusedFile", session.focusedFile);
                sessionElement.addContent(filesElement);
                sessionsElement.addContent(sessionElement);
            }
            element.addContent(sessionsElement);

            return element;
        }

    ...

    }

That's working just fine and generates the target file `tabsession.xml`:

    <?xml version="1.0" encoding="UTF-8"?>
    <project version="4">
      <component name="SessionConfiguration">
        <state version="1" />
        <sessions>
          <session name="first">
            <files focusedFile="$PROJECT_DIR$/src/First.java">
              <file path="$PROJECT_DIR$/src/First.java" />
              <file path="$PROJECT_DIR$/src/Second.java" />
            </files>
          </session>
        </sessions>
      </component>
    </project>

But if the state gets saved again with different data, old lines are not removed. For example, if i open another file and the state gets saved the xml looks like this:

    <?xml version="1.0" encoding="UTF-8"?>
    <project version="4">
      <component name="SessionConfiguration">
        <state version="1" />
        <sessions>
          <session name="first">
            <files focusedFile="$PROJECT_DIR$/src/First.java">
              <file path="$PROJECT_DIR$/src/First.java" />
              <file path="$PROJECT_DIR$/src/Second.java" />
              <file path="$PROJECT_DIR$/src/First.java" />
              <file path="$PROJECT_DIR$/src/Second.java" />
              <file path="$PROJECT_DIR$/src/Third.java" />
            </files>
          </session>
        </sessions>
      </component>
    </project>

Which is clearly wrong. Any ideas how i can save only the current state while removing old lines?