Index: jackrabbit-core/src/main/java/org/apache/jackrabbit/core/state/LocalItemStateManager.java
===================================================================
--- jackrabbit-core/src/main/java/org/apache/jackrabbit/core/state/LocalItemStateManager.java	(revision 793243)
+++ jackrabbit-core/src/main/java/org/apache/jackrabbit/core/state/LocalItemStateManager.java	Mon Aug 31 13:56:25 CEST 2009
@@ -407,11 +407,21 @@
             try {
                 local = changeLog.get(created.getId());
                 if (local != null) {
+                    if (local.isNode() && local.getOverlayedState() != created) {
+                        // mid-air collision of concurrent node state creation
+                        // with same id (JCR-2272)
+                        if (local.getStatus() == ItemState.STATUS_NEW) {
+                            local.setStatus(ItemState.STATUS_STALE_MODIFIED);
+                        }
+                    } else {
+                        if (local.getOverlayedState() == created) {
-                    // underlying state has been permanently created
-                    local.pull();
-                    local.setStatus(ItemState.STATUS_EXISTING);
-                    cache.cache(local);
-                }
+                            // underlying state has been permanently created
+                            local.pull();
+                            local.setStatus(ItemState.STATUS_EXISTING);
+                            cache.cache(local);
+                        }
+                    }
+                }
             } catch (NoSuchItemStateException e) {
                 /* ignore */
             }
Index: jackrabbit-core/src/main/java/org/apache/jackrabbit/core/state/SharedItemStateManager.java
===================================================================
--- jackrabbit-core/src/main/java/org/apache/jackrabbit/core/state/SharedItemStateManager.java	(revision 803470)
+++ jackrabbit-core/src/main/java/org/apache/jackrabbit/core/state/SharedItemStateManager.java	Mon Aug 31 13:49:39 CEST 2009
@@ -20,6 +20,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Set;
+import java.util.Calendar;
 
 import javax.jcr.PropertyType;
 import javax.jcr.ReferentialIntegrityException;
@@ -48,6 +49,7 @@
 import org.apache.jackrabbit.core.virtual.VirtualItemStateProvider;
 import org.apache.jackrabbit.spi.Name;
 import org.apache.jackrabbit.spi.commons.name.NameConstants;
+import org.apache.jackrabbit.JcrConstants;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -631,7 +633,7 @@
                                                 return false;
                                             }
                                             NodeDef def = ntReg.getNodeDef(ns.getDefinitionId());
-                                            return def != null ? def.allowsSameNameSiblings() : false;
+                                            return def != null && def.allowsSameNameSiblings();
                                         }
                                     };
 
@@ -660,6 +662,14 @@
                     shared.deleted(state.getOverlayedState());
                 }
                 for (ItemState state : local.addedStates()) {
+                    if (state.isNode() && state.getStatus() != ItemState.STATUS_NEW) {
+                        // another node with same id had been created
+                        // in the meantime, probably caused by mid-air collision
+                        // of concurrent versioning operations (JCR-2272)
+                        String msg = state.getId() + " has been created externally";
+                        log.debug(msg);
+                        throw new StaleItemStateException(msg);
+                    }
                     state.connect(createInstance(state));
                     shared.added(state.getOverlayedState());
                 }