memcached events are being logged to ns_server logs, memcached logs are empty

We have a cluster running from last 12 hrs+, the cluster is not idle, and is being continually under testing.

But, we are seeing memcached logs being empty.

For example, (a snippet of logs)
Seeing that the memcached is logging to info in ns_server logs.

[ns_server:info,2012-08-19T23:49:52.968,ns_1@10.3.121.24:ns_port_memcached:ns_port_server:log:169]memcached<0.513.0>: 4379 3: Warning: failed to retrieve key value from database, name=/data/default-s/345.couch.6 key=1-ec90c48df0344bd7 error=document not found errno=none deleted=yes
memcached<0.513.0>: 4380 3: Warning: failed to retrieve key value from database, name=/data/default-s/345.couch.6 key=1-de9f474c574e0466 error=document not found errno=none deleted=yes
memcached<0.513.0>: 4380 3: Warning: failed to retrieve key value from database, name=/data/default-s/345.couch.6 key=1-db157b2a71cafd78 error=document not found errno=none deleted=yes
memcached<0.513.0>: 4380 3: Warning: failed to retrieve key value from database, name=/data/default-s/345.couch.6 key=1-b3b79b801a9e0afd error=document not found errno=none deleted=yes

du -skh /opt/couchbase/var/lib/couchbase/log/*
4.0K memcached.log.0.gz
4.0K memcached.log.1.gz
0 memcached.log.2.gz
0 memcached.log.3.gz

Also, the memcached.log.0.gz and memcached.log.1.gz are almost always empty.

/opt/couchbase/bin/memcached -X /opt/couchbase/lib/memcached/stdin_term_handler.so -X /opt/couchbase/lib/memcached/file_logger.so,filename=/opt/couchbase/var/lib/couchbase/log/memcached.log -l 0.0.0.0:11210,0.0.0.0:11209:1000 -p 11210 -E /opt/couchbase/lib/memcached/bucket_engine.so -B binary -r -c 10000 -e admin=_admin;default_bucket_name=default;auto_create=false

Something to note, we are not seeing this always.