stats.numRemainingBgJobs in Ep-engine code is not updated correctly

With 5 buckets on the same server node, even without any client workload, the memcached runs 50% of CPU means making 2 CPUs busy in 4 CPU box.
While running gdb, it shows that stats.numRemainingBgJobs is not updated correctly.

Here is the snapshot of the perf output:
19.88% memcached ep.so [.] VBucketMap::getBucket(unsigned short) const
12.31% memcached ep.so [.] BgFetcher::run(SingleThreadedRCPtr<Task>&)
11.81% memcached libpthread-2.12.so [.] pthread_mutex_lock
9.44% memcached ep.so [.] SpinLock::acquire()
6.60% memcached libpthread-2.12.so [.] pthread_mutex_unlock
6.39% memcached ep.so [.] VBucket::getBGFetchItems(std::tr1::unordered_map<unsigned long, std::list<VBucketBGFetchItem*, std::allocator<VBucketBGFetchItem*> >, std::tr1::hash<u
4.59% memcached ep.so [.] Mutex::release()
2.15% memcached ep.so [.] SpinLock::release()
1.80% memcached ep.so [.] Dispatcher::moveReadyTasks(timeval const&)
1.73% memcached ep.so [.] Mutex::acquire()
1.49% memcached ep.so [.] SpinLock::~SpinLock()