Unfortunately this seems to cause a lot of memcache exceptions like

com.google.appengine.api.memcache.MemcacheServiceException: Memcache getAll: exception getting multiple keys
at com.google.appengine.api.memcache.MemcacheServiceApiHelper$RpcResponseHandler.handleApiProxyException (MemcacheServiceApiHelper.java:69)
at com.google.appengine.api.memcache.MemcacheServiceApiHelper$1.absorbParentException (MemcacheServiceApiHelper.java:111)
at com.google.appengine.api.utils.FutureWrapper.handleParentException (FutureWrapper.java:52)
at com.google.appengine.api.utils.FutureWrapper.get (FutureWrapper.java:91)
at com.google.appengine.api.memcache.MemcacheServiceImpl.quietGet (MemcacheServiceImpl.java:26)
at com.google.appengine.api.memcache.MemcacheServiceImpl.getAll (MemcacheServiceImpl.java:64)
at com.googlecode.objectify.cache.KeyMemcacheService.getAll (KeyMemcacheService.java:87)
at com.googlecode.objectify.cache.EntityMemcache.cacheGetAll (EntityMemcache.java:353)
at com.googlecode.objectify.cache.EntityMemcache.putAll (EntityMemcache.java:292)
at com.googlecode.objectify.cache.CachingAsyncDatastoreService$3.success (CachingAsyncDatastoreService.java:279)
at com.googlecode.objectify.cache.CachingAsyncDatastoreService$3.success (CachingAsyncDatastoreService.java:1)
at com.googlecode.objectify.cache.TriggerSuccessFuture.trigger (TriggerSuccessFuture.java:37)
at com.googlecode.objectify.cache.TriggerFuture.isDone (TriggerFuture.java:87)
at com.googlecode.objectify.cache.TriggerFuture.get (TriggerFuture.java:102)
at com.googlecode.objectify.util.FutureHelper.quietGet (FutureHelper.java:26)
at com.googlecode.objectify.cache.CachingDatastoreService.get (CachingDatastoreService.java:161)
at com.googlecode.objectify.cache.CachingDatastoreService.get (CachingDatastoreService.java:147)
at com.googlecode.objectify.cache.CachingDatastoreService.get (CachingDatastoreService.java:128)