some of the stats does a counter underflow after membase is restarted

Run the below script on a fresh membase server.

<?php

$mc = new memcache();
$mc->addserver("localhost", 11211);

for ($i=0; $i< 10 ; $i++)

?>

restart membase server.

Following stats have a high value after restart:
STAT ep_commit_time_total 2994613510
STAT ep_flush_duration 2994613510
STAT ep_flush_duration_total 2994613510
STAT ep_flush_duration_highwat 2994613510