Following scenario:

public class MyService {
    @Inject
    private EntityManager em; // injects a WELD proxy

    public void test() {
          em.unwrap(org.hibernate.engine.spi.SessionImplementor.class).getFactory();
    }
}

Calling MyService#test results in a ClassCastException:

java.lang.ClassCastException: org.jboss.weldx.persistence.EntityManager$470189163$Proxy$_$$_WeldClientProxy cannot be cast to org.hibernate.engine.spi.SessionImplementor

This is becuase the condition at org.jboss.weld.bean.proxy.ProxyMethodHandler:103 causes the method handler to return self instead of this. The return type of EntityManager#unwrap is unbounded generic so

thisMethod.getReturnType().isAssignableFrom(self.getClass()))

always is true.