Hello,
I have come upon this issue on a partially-Groovy war deployment on Wildfly 8.1.0.Final, which uses Hibernate Validator 5.1.0. I have debugged the HV code, found the offending bean and after I converted its superclass to plain Java the issue was gone. So this is probably related to some bytecode-magic Groovy does (synthetic methods as well?). But still it would be nice if Hibernate Validator (and thus Wildfly/JBoss) didn't crash on Groovy apps. I can provide a sample war deployment that fails with this error message on Wildfly 8.1.0.Final