The JTop plugin includes this code:
    public void setMBeanServerConnection(MBeanServerConnection mbs) {
        this.server = mbs;
        try {
            this.tmbean = newPlatformMXBeanProxy(server,
                                                 THREAD_MXBEAN_NAME,
                                                 ThreadMXBean.class);
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (!tmbean.isThreadCpuTimeSupported()) {
            System.err.println("This VM does not support thread CPU time monitor
ing");
        } else {
            tmbean.setThreadCpuTimeEnabled(true);
        }
    }

Notice the line tmbean This triggers bug 6696970 which causes JConsole to become unusable for the connection as a whole. If 6696970 is fixed then it might be reasonable to throw an exception (which JConsole will presumably display in a dialog window), but it would be better for JTop to catch the exception and operate in a degraded mode where it doesn't show CPU times (but does still show the list of threads).