Index: src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java
===================================================================
--- src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java	(revision 1592627)
+++ src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java	(working copy)
@@ -1307,7 +1307,18 @@
                 i++;
             }
             names.setDefinedNameArray(nr);
+            if(workbook.isSetDefinedNames()) {
+                workbook.unsetDefinedNames();
+            }
             workbook.setDefinedNames(names);
+            
+            // Re-process the named ranges
+            namedRanges = new ArrayList<XSSFName>();
+            if(workbook.isSetDefinedNames()) {
+                for(CTDefinedName ctName : workbook.getDefinedNames().getDefinedNameArray()) {
+                    namedRanges.add(new XSSFName(ctName, this));
+                }
+            }
         } else {
             if(workbook.isSetDefinedNames()) {
                 workbook.unsetDefinedNames();