Without ACC_SUPER (or ACC_IDENTITY) set, synchronized method breaks CFP:

public class SyncMethod {
    synchronized int testMethod() { return 0; }
}

Certain JCK tests like ireturn00601m1 fail because of this.

The code in ClassFileParser::verify_legal_method_modifiers()

----
if (!is_identity_class && is_synchronized && !is_static) {
  is_illegal = true;
...
----

breaks it's loading. Intention may have been:
 "(!is_identity_class && is_value_class && is_synchronized && !is_static)"