Strange behavior when one node is down

I'm testing our php app in couchbase as a drop-in replacement for memcache. I didn't change the code, so still using pecl/memcache extension (note I use memcache extension, without "d").

Actually detect a issue when a node go down.
This is the case:

- Couchbase 1.8.1 Enterprise Edition, 3 node cluster (A,B,C), automatic failover (30 seconds).
- Storing on couchbase bucket-type with replication (1 copy) on port 11214
- Cliente: PHP 5.3.2 with PECL/memcache 2.2.5

- Test case:
* php script:
+ Set 10 key/values. Use this code to connect (I use addServer as I used on memcache; i know this is not necessary):

      (...)
      $memcache = new Memcache;
      $memcache->addServer('A',11214);
      $memcache->addServer('B',11214);
      $memcache->addServer('C',11214);
      for ($i=1;$i<=10;$i++) {
          $memcache->set('key_'.$i,'content of key '.$i,false,3600) or die ("Fail to set");
      };
      (...)
 

+ Loop 1000 times with one second sleep:

      (...)
      for ($a=1;$a<=1000;$a++) {
         $memcache_r = new Memcache;
         $memcache_r->addServer('A',11214);
         for ($i=1;$i<=10;$i++) {
             echo $memcache->get('key_'.$i);
         };
         $memcache_r->close();
         unset($memcache_r);
         sleep(1);
      }
      (...)
 

I start running this code and see every one second all the keys printed.
I'm let the script to run several seconds (I'm assured than all the sets go ok and I get all the keys at least once) and shutdown couchbase on server B.
Now, the strange behavior:
- Since couchbase on server B is shutted down, I get two types of results:
* result 1: Fail all gets
* result 2: Get ok only one key, and the rest of keys fail.

I get this results randomly, for example, I get 3 "result 1", then 1 "result 2", then 2 "result 1" an so.
- 30 seconds later, couchbase mark server B down, make automatic failover and all the keys printed again.

Is this a normal behavior?
This is because I am using memcache libraries?
When server B is down, why sometimes get result and sometimes not? I expected not to get some keys (keys who are living on server B), but I get sometimes one get ok and sometimes all the get fails. And I don't know why.

Thanks in advance

Fernando.-