When you create a Seam 2.2 EAR project and deploy it to EAP 5.1.2 it cannot be properly removed - if you select both the ear and the -ds.xml in the server view and press Delete, they will be first both undeployed, but right after that the ear will be deployed again and will fail to do so without the datasource.
So the main problem is that even after removing everything from the server, the ear project somehow is still there in the deploy directory.