=== modified file 'bin/osv/fields.py'
--- bin/osv/fields.py	2010-08-10 09:47:21 +0000
+++ bin/osv/fields.py	2010-08-16 10:15:21 +0000
@@ -424,7 +424,8 @@
             res[id] = []
         ids2 = obj.pool.get(self._obj).search(cr, user, [(self._fields_id, 'in', ids)], limit=self._limit, context=context)
         for r in obj.pool.get(self._obj)._read_flat(cr, user, ids2, [self._fields_id], context=context, load='_classic_write'):
-            res[r[self._fields_id]].append(r['id'])
+            if r[self._fields_id] in res:
+                res[r[self._fields_id]].append(r['id'])
         return res
 
     def set(self, cr, obj, id, field, values, user=None, context=None):