Index: questiontype.php
===================================================================
RCS file: /cvsroot/moodle/contrib/plugins/question/type/matrix/Attic/questiontype.php,v
retrieving revision 1.1.2.6
diff -u -r1.1.2.6 questiontype.php
--- questiontype.php	15 Apr 2009 10:39:53 -0000	1.1.2.6
+++ questiontype.php	27 Aug 2010 15:52:22 -0000
@@ -306,8 +306,13 @@
     }
 
     function compare_responses($question, $state, $teststate) {
-        return (count(array_diff($state->responses, $teststate->responses))  == 0
-            && count(array_diff($teststate->responses, $state->responses)) == 0);
+        if ($question->options->multiple) {
+            return (count(array_diff(array_keys($state->responses), array_keys($teststate->responses)))  == 0
+              && count(array_diff(array_keys($teststate->responses), array_keys($state->responses))) == 0);
+        } else {
+            return (count(array_diff_assoc($state->responses, $teststate->responses))  == 0
+                && count(array_diff_assoc($teststate->responses, $state->responses)) == 0);
+        }
     }
 
     function get_actual_response($question, $state) {