Persisting app.config variables in updates via Click once deployment

Every time a new update is released for an application with click once, the variables in the app.config file are destroyed

<userSettings>
    <app.My.MySettings>
      <setting name="Email" serializeAs="String">
        <value />
      </setting>
      <setting name="UserName" serializeAs="String">
        <value />
      </setting>
    </app.My.MySettings>
  </userSettings>

How can i prevent that?

Is there any way of feching the variables from the previous application version?