diff -r ad3b9bde4308 xml.wsdl.model/src/org/netbeans/modules/xml/wsdl/model/impl/WSDLModelImpl.java
--- a/xml.wsdl.model/src/org/netbeans/modules/xml/wsdl/model/impl/WSDLModelImpl.java	Fri May 14 16:52:14 2010 +0400
+++ b/xml.wsdl.model/src/org/netbeans/modules/xml/wsdl/model/impl/WSDLModelImpl.java	Mon May 17 22:45:41 2010 +0400
@@ -245,16 +255,20 @@
         return getElementRegistry().getKnownElementNames();
     }
     
-    public ChangeInfo prepareChangeInfo(List<Node> pathToRoot) {
-        ChangeInfo change = super.prepareChangeInfo(pathToRoot);
+    @Override
+    public ChangeInfo prepareChangeInfo(List<? extends Node> pathToRoot,
+            List<? extends Node> nsContextPathToRoot) {
+        ChangeInfo change = super.prepareChangeInfo(pathToRoot, nsContextPathToRoot);
         DocumentComponent parentComponent = findComponent(change.getRootToParentPath());
         if (parentComponent == null) {
             return change;


diff -r ad3b9bde4308 xml.xam/apichanges.xml
--- a/xml.xam/apichanges.xml	Fri May 14 16:52:14 2010 +0400
+++ b/xml.xam/apichanges.xml	Mon May 17 22:45:41 2010 +0400
@@ -104,6 +104,25 @@
     <!-- ACTUAL CHANGES BEGIN HERE: -->
     <changes>
         
+        <change id="fix_issue_166177">
+            <api name="org.netbeans.modules.xml.xam"/>
+            <summary>Method AbstractDocumentModel.prepareChangeInfo() is replaced with a new one.</summary>
+            <version major="1.10" minor="1"/>
+            <date day="19" month="5" year="2010"/>
+            <author login="supernikita"/>
+            <compatibility binary="compatible" source="compatible" addition="yes"/>
+            <description>
+                The modufication is necessary for fixing issue #166177.
+                The old method {@link org.netbeans.modules.xml.xam.dom.AbstractDocumentModel#prepareChangeInfo(java.util.List)}
+                is marked as deprecated and a new one {@link org.netbeans.modules.xml.xam.dom.AbstractDocumentModel#prepareChangeInfo(java.util.List, java.util.List)} is created.
+                The new one contains additional parameter <code>nsContextPathToRoot</code>, which
+                is necessary for correct calculation of namespace context after
+                deletion of namespace prefix. See the issue for details. 
+            </description>
+            <class package="org.netbeans.modules.xml.xam.dom" name="AbstractDocumentModel"/>
+            <issue number="166177"/>
+        </change>
+
         <change id="model-changes-notification">
             <api name="org.netbeans.modules.xml.xam"/>
             <summary>Two new methods to enhance model's performance</summary>


diff -r ad3b9bde4308 xml.xam/src/org/netbeans/modules/xml/xam/dom/AbstractDocumentModel.java
--- a/xml.xam/src/org/netbeans/modules/xml/xam/dom/AbstractDocumentModel.java	Fri May 14 16:52:14 2010 +0400
+++ b/xml.xam/src/org/netbeans/modules/xml/xam/dom/AbstractDocumentModel.java	Mon May 17 22:45:41 2010 +0400
@@ -225,13 +225,36 @@
     }
 
     /**
-     * Performs preparation stage of synchronization XDM --> XAM.
      *
-     * Be aware that the method isn't only called from XDM (XDMListener),
-     * but it also can be redifined. An example can be found in WSDL Model. 
+     * @param pathToRoot
+     * @return
+     * @deprecated Use {@link org.netbeans.modules.xml.xam.dom.AbstractDocumentModel#prepareChangeInfo(java.util.List, java.util.List)} instead. It is necessary for fixing bug #166177.
      *
      */
     public ChangeInfo prepareChangeInfo(List<Node> pathToRoot) {
+        return prepareChangeInfo(pathToRoot, pathToRoot);
+    }
+
+
+    /**
+     * Performs intermediate stage of synchronization XDM --> XAM.
+     * A new {@link org.netbeans.modules.xml.xam.dom.ChangeInfo} object 
+     * is generated here.
+     *
+     * @param pathToRoot a path of DOM objects from root to changed one.
+     * @param nsContextPathToRoot Usually the same path as previous param,
+     * but in case of deletion it contains the same path from old model's tree.
+     * It is required in case of prefix declaration deletion, because the deleted
+     * declaration is present only in old model's tree.
+     *
+     * Be aware that the method is designed to be called only from XDM
+     * {@link org.netbeans.modules.xml.xdm.xam.XDMListener},
+     * but it also can be redifined. An example can be found in
+     * {@link org.netbeans.modules.xml.wsdl.model.WSDLModel}.
+     *
+     */
+    public ChangeInfo prepareChangeInfo(List<? extends Node> pathToRoot,
+            List<? extends Node> nsContextPathToRoot) {
         // we already handle change on root before enter here
         if (pathToRoot.size() < 1) {
             throw new IllegalArgumentException("pathToRoot here should be at least 1");
@@ -261,7 +284,7 @@
                 }
 
                 QName currentQName = new QName(getAccess().lookupNamespaceURI(
-                        current, pathToRoot), current.getLocalName());
+                        current, nsContextPathToRoot), current.getLocalName());
                 if (!(qnames.contains(currentQName))) {
                     changedIsDomainElement =  false;
                     break;


diff -r ad3b9bde4308 xml.xdm/src/org/netbeans/modules/xml/xdm/xam/XDMListener.java
--- a/xml.xdm/src/org/netbeans/modules/xml/xdm/xam/XDMListener.java	Fri May 14 16:52:14 2010 +0400
+++ b/xml.xdm/src/org/netbeans/modules/xml/xdm/xam/XDMListener.java	Mon May 17 22:45:41 2010 +0400
@@ -182,9 +180,7 @@
                 assert namespacePathToRoot.size() == pathToRoot.size();
             }
             //
-            ChangeInfo change = model.prepareChangeInfo(pathToRoot);
+            ChangeInfo change = model.prepareChangeInfo(pathToRoot, namespacePathToRoot);
             change.setAdded(isAdded);
             processChange(change);
         }