The explanation is actually in the conf/jboss-service.xml file.
You'd replace the deployment sorter for the URLComparator tag:
If the name portion of the url begins with 1 or more digits, those digits are converted to an int (ignoring leading zeroes), and files are deployed in that order. Files that do not start with any digits will be deployed first, and they will be sorted by extension as above with DeploymentSorter.
thank you for your tip. I tried this, but it didn't work.
But now I know what was the problem. I was thinking in the wrong direction.
I just had to add this line in the farm-service.xml to get rid of the problem:
Then my .jar had all the informations that are necessary for its deployment.
Thank you very much.