Index: core/src/com/icesoft/faces/context/BridgeFacesContext.java
===================================================================
--- core/src/com/icesoft/faces/context/BridgeFacesContext.java	(revision 124)
+++ core/src/com/icesoft/faces/context/BridgeFacesContext.java	(working copy)
@@ -88,6 +88,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Vector;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.regex.Pattern;
 
 public class
@@ -131,6 +132,7 @@
             viewRoot = null;
         }
     };
+    private final ReentrantLock serializerLock = new ReentrantLock();
 
     private static Constructor jsfUnitConstructor;
     private static String jsfUnitClass;
@@ -313,16 +315,34 @@
         return responseWriter = new DOMResponseWriter(this, domSerializer, configuration, jsCodeURIs, cssRuleURIs, blockingRequestHandlerContext);
     }
 
+    void lockSerializer() {
+        serializerLock.lock();
+    }
+
+    void unlockSerializer() {
+        serializerLock.unlock();
+    }
+
     public void switchToNormalMode() throws Exception {
-        externalContext.switchToNormalMode();
-        domSerializer = new SaveCurrentDocument(new NormalModeSerializer(this, externalContext.getWriter("UTF-8")));
+        lockSerializer();
+        try {
+            externalContext.switchToNormalMode();
+            domSerializer = new SaveCurrentDocument(new NormalModeSerializer(this, externalContext.getWriter("UTF-8")));
+        } finally {
+            unlockSerializer();
+        }
     }
 
     public void switchToPushMode() throws Exception {
-        //collect bundles put by Tag components when the page is parsed
-        bundles = externalContext.collectBundles();
-        externalContext.switchToPushMode();
-        domSerializer = new SaveCurrentDocument(new PushModeSerializer(documentStore, view, this, viewNumber));
+        lockSerializer();
+        try {
+            //collect bundles put by Tag components when the page is parsed
+            bundles = externalContext.collectBundles();
+            externalContext.switchToPushMode();
+            domSerializer = new SaveCurrentDocument(new PushModeSerializer(documentStore, view, this, viewNumber));
+        } finally {
+            unlockSerializer();
+        }
     }
 
     public UIViewRoot getViewRoot() {
@@ -336,7 +356,7 @@
 
     public void setViewRoot(UIViewRoot viewRoot) {
         // #3424. Allow viewRoot to be set to null. On page reload, this object
-        // is reused, but viewRoot must be nullable 
+        // is reused, but viewRoot must be nullable
         this.viewRoot = viewRoot;
         if (viewRoot != null) {
             lastViewID = viewRoot.getViewId();
@@ -529,7 +549,7 @@
                                 }
                             }
                             if (found) {
-                                // For some reason, our multiple checkbox 
+                                // For some reason, our multiple checkbox
                                 // components use checked="true", while
                                 // our single checkbox components use
                                 // checked="checked". The latter complying
@@ -868,7 +888,7 @@
         void save(Document document) throws IOException;
 
         /* Keep the Document in a more efficient form for
-           fast loading 
+           fast loading
         */
         void cache(Document document) throws IOException;
 
Index: core/src/com/icesoft/faces/context/NormalModeSerializer.java
===================================================================
--- core/src/com/icesoft/faces/context/NormalModeSerializer.java	(revision 124)
+++ core/src/com/icesoft/faces/context/NormalModeSerializer.java	(working copy)
@@ -53,7 +53,16 @@
     }
 
     public void serialize(Document document) throws IOException {
+        context.lockSerializer();
         try {
+            doSerialization(document);
+        } finally {
+            context.unlockSerializer();
+        }
+    }
+    
+    private void doSerialization(Document document) throws IOException {
+        try {
             if (context.isContentIncluded()) {
                 if (log.isDebugEnabled()) {
                     log.debug("treating request as a fragment");
Index: core/src/com/icesoft/faces/context/PushModeSerializer.java
===================================================================
--- core/src/com/icesoft/faces/context/PushModeSerializer.java	(revision 124)
+++ core/src/com/icesoft/faces/context/PushModeSerializer.java	(working copy)
@@ -66,6 +66,15 @@
     }
 
     public void serialize(final Document document) throws IOException {
+        context.lockSerializer();
+        try {
+            doSerialization(document);
+        } finally {
+            context.unlockSerializer();
+        }
+    } 
+    
+    private void doSerialization(Document document) throws IOException {
         Node[] changed = DOMUtils.domDiff(store.load(), document);
         HashMap depthMaps = new HashMap();
         for (int i = 0; i < changed.length; i++) {