Make sure the right "ignore" deployer is present.
How can I do this?
An AbstractIgnoreDeployer should be present in deployers.xml.
I added jboss-ignore.txt to core.jar/META-INF/ with following content:
core.jar/META-INF/persistence.xml
Nothing changed.
It should be w/o core.jar/, since it's relative to that (sub)deployment.