JMX on Kafka 0.8.1

Hi

I'm trying to get some JMX stats from a running Kafka instance, I can
connect using jconsole and I can see various topic specific information, I
can see the "..LogEndOffset" value changing as I add data, but for some
reason the value for

"kafka.server":type="BrokerTopicMetrics",name="AllTopicsBytesInPerSec"
"kafka.server":type="BrokerTopicMetrics",name="AllTopicsBytesOutPerSec"
...

Always show zero. This strikes me as strange, I didn't think there would be
enable/disable feature for this, anyone have any ideas why this might be?

Thanks!!
Jinder