Google App Engine dynamic backends are not stopped
===

(If this is not a question for SO, I will be gladly moved elsewhere)

I have a GAE backend that I want to start regularly with cron. With the help of other questions from SO, I set up backends.xml like this 

    <?xml version="1.0" encoding="UTF-8"?>
    <backends>
     <backend name="myBackend">
       <class>B1</class>
       <instances>1</instances>
    <options>
         <dynamic>true</dynamic>
       </options>
     </backend>
    </backends>

and my cron.xml like this

    <?xml version="1.0" encoding="UTF-8"?>
    <cronentries>
      <cron>
        <url>/doHardStuff</url>
        <description>doing long running stuff</description>
        <schedule>every 3 hours</schedule>
        <target>myBackend</target>
      </cron>
    </cronentries>

And I upload it using `mvn-gae` (I am writing everything in java with maven) with goals `gae:deploy gae:backends-list gae:backends-update`

Everything loads fine and the long running stuff is done, **however**. Even after finishing everything, the dynamic backend still runs and eats my daily backend quota. I can see `_ah/stop` request in logs after the servlet finishes its job; however the backend still runs after that.

If I **stop** it manually in engine web console in Main -> Backends -> Start/Stop, it stops eating my quota, however, it **won't** run at a given time in cron and the cron job will fail.

What should I do? I want the backend to *start at the given time* and *stop when the request is over and the machine is idle*. I don't want it running at a different time.