=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/dataelement/DataElementOperand.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/dataelement/DataElementOperand.java	2014-08-15 07:40:20 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/dataelement/DataElementOperand.java	2014-11-18 11:35:52 +0000
@@ -253,9 +253,11 @@
      */
     public Integer getRelevantAggregationLevel( int organisationUnitLevel )
     {
-        Collections.sort( aggregationLevels );
+        List<Integer> levels = new ArrayList<>( aggregationLevels );
+        
+        Collections.sort( levels );
 
-        for ( final Integer aggregationLevel : aggregationLevels )
+        for ( final Integer aggregationLevel : levels )
         {
             if ( aggregationLevel >= organisationUnitLevel )
             {