alerts despite Black Out

We're monitoring specific middleware (eBS ERP) with OEM 13.2 and we are seeing this behavior:

1. Enable blackout on all components which are part of that set of middleware software - then wait some minutes

2. Actually stop that middleware software

3. We see no alerts being raised, no mails being sent

4. A lot of time goes by

5. We start the same software as stopped in step 2

6. For debugging purpose, we wait for at least 30 minutes, or better 1 hour

7. We disable blackout

Result: after step 7 is performed, we get messages (mails) stating software is down. If you click on the URL's of those messages however, it says the current status is : Up