[204618] Unable to set "required" use option in XSD design view when adding attribute reference

diff --git a/bundles/org.eclipse.wst.xsd.ui/src-common/org/eclipse/wst/xsd/ui/internal/common/properties/sections/XSDAttributeDeclarationSection.java b/bundles/org.eclipse.wst.xsd.ui/src-common/org/eclipse/wst/xsd/ui/internal/common/properties/sections/XSDAttributeDeclarationSection.java
index 2507e7e..ce46a7f 100644
--- a/bundles/org.eclipse.wst.xsd.ui/src-common/org/eclipse/wst/xsd/ui/internal/common/properties/sections/XSDAttributeDeclarationSection.java
+++ b/bundles/org.eclipse.wst.xsd.ui/src-common/org/eclipse/wst/xsd/ui/internal/common/properties/sections/XSDAttributeDeclarationSection.java

@@ -326,9 +326,9 @@
     {
       if (input instanceof XSDAttributeDeclaration)
       {
-        XSDAttributeDeclaration xsdAttribute = ((XSDAttributeDeclaration) input).getResolvedAttributeDeclaration();
+        XSDAttributeDeclaration xsdAttribute = (XSDAttributeDeclaration) input;
         isAttributeReference = ((XSDAttributeDeclaration)input).isAttributeDeclarationReference();
-        XSDTypeDefinition typeDef = xsdAttribute.getTypeDefinition();
+        XSDTypeDefinition typeDef = xsdAttribute.getResolvedAttributeDeclaration().getTypeDefinition();
         boolean isAnonymous = xsdAttribute.getAnonymousTypeDefinition() != null;
 
         if (isAnonymous)
@@ -401,7 +401,7 @@
         }
         
         formCombo.setText(""); 
-        formCombo.setEnabled(!xsdAttribute.isGlobal());
+        formCombo.setEnabled(!xsdAttribute.isGlobal() && !isAttributeReference);
         boolean hasFormAttribute = false;
         if (element != null)
         {