Hmm. Looks pretty good. (The QualificationRealm also needs a cache-type of "infinispan" but I guess you have tried that).
Aside from that, I think it may be a case of attaching the debugger to JBoss, and step through the JBoss code to figure out what is going on. I can't remember the exact class name, think it might be JBossCachedAuthenticationManager.