UPDATE:

Google once again struck down on our site, and found a backdoor to clicking the arrows on our tasklist . This again causes many tasks to be seen as updated by the site. I adapted the robots.txt again, it should now no loinger happen. I can only wait untill the next crawl to verify this...
On the good side: we now have most of our pages in google: Click here to see our pages on google.  read more »