Shutdown method hangs

We have a small round robin pool of MemcachedClient objects.
On application shutdown we do call shutdown on each MemcachedClient,but it hangs and application shutdown hangs too.
Do you have any ideas why?

I have a thread dump

   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for <0x0000000700b24368> (a java.util.concurrent.CountDownLatch$Sync)
        at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:198)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedNanos(AbstractQueuedSynchronizer.java:1011)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(AbstractQueuedSynchronizer.java:1303)
        at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:253)
        at net.spy.memcached.MemcachedClient.waitForQueues(MemcachedClient.java:2120)
        at net.spy.memcached.MemcachedClient.shutdown(MemcachedClient.java:2073)