diff -r 460e37d40f12 -r acaa49a2768a jdk/src/share/classes/javax/management/modelmbean/ModelMBeanInfoSupport.java
--- a/jdk/src/share/classes/javax/management/modelmbean/ModelMBeanInfoSupport.java	Wed Oct 21 16:28:57 2009 +0200
+++ b/jdk/src/share/classes/javax/management/modelmbean/ModelMBeanInfoSupport.java	Wed Oct 21 17:33:18 2009 +0200
@@ -945,7 +945,8 @@
      */
     private Descriptor validDescriptor(final Descriptor in) throws RuntimeOperationsException {
         Descriptor clone;
-        if (in == null) {
+        boolean defaulted = (in == null);
+        if (defaulted) {
             clone = new DescriptorSupport();
             MODELMBEAN_LOGGER.finer("Null Descriptor, creating new.");
         } else {
@@ -953,11 +954,11 @@
         }
 
         //Setting defaults.
-        if (clone.getFieldValue("name")==null) {
+        if (defaulted && clone.getFieldValue("name")==null) {
             clone.setField("name", this.getClassName());
             MODELMBEAN_LOGGER.finer("Defaulting Descriptor name to " + this.getClassName());
         }
-        if (clone.getFieldValue("descriptorType")==null) {
+        if (defaulted && clone.getFieldValue("descriptorType")==null) {
             clone.setField("descriptorType", MMB);
             MODELMBEAN_LOGGER.finer("Defaulting descriptorType to \"" + MMB + "\"");
         }