Index: src/main/java/org/apache/jackrabbit/core/state/ItemStateReferenceCache.java
===================================================================
--- src/main/java/org/apache/jackrabbit/core/state/ItemStateReferenceCache.java	(revision 1354517)
+++ src/main/java/org/apache/jackrabbit/core/state/ItemStateReferenceCache.java	(working copy)
@@ -172,10 +172,11 @@
         ItemId id = state.getId();
         Map<ItemId, ItemState> segment = getSegment(id);
         synchronized (segment) {
-            if (segment.containsKey(id)) {
+            ItemState s = segment.put(id, state);
+            // overwriting the same instance is OK
+            if (s != null && s != state) {
                 log.warn("overwriting cached entry " + id);
             }
-            segment.put(id, state);
         }
     }
 
Index: src/main/java/org/apache/jackrabbit/core/state/SharedItemStateManager.java
===================================================================
--- src/main/java/org/apache/jackrabbit/core/state/SharedItemStateManager.java	(revision 1354517)
+++ src/main/java/org/apache/jackrabbit/core/state/SharedItemStateManager.java	(working copy)
@@ -787,6 +787,17 @@
 
             ISMLocking.ReadLock readLock = null;
             try {
+                // make sure new item states are present/referenced in cache
+                // we do this before the lock is downgraded to a read lock
+                // because then other threads will be able to read from
+                // this SISM again and potentially read an added item state
+                // before the ones here are put into the cache (via
+                // shared.persisted()). See JCR-3345
+                for (ItemState state : shared.addedStates()) {
+                    state.setStatus(ItemState.STATUS_EXISTING);
+                    cache.cache(state);
+                }
+
                 // downgrade to read lock
                 readLock = writeLock.downgrade();
                 writeLock = null;