We had a configuration of 3 computers:
computer A: domain-controller, host-controller
computer B: host
computer C: host

host.xml <servers> element was empty for each host. When adding a jboss-as server instance to host C using the web console (domain-controller) it mistakenly got written to host B, supposedly because host B was added earlier to the cluster, instead to writing it to host C's host.xml file.