Index: DicomAttributeCollection.cs
===================================================================
--- DicomAttributeCollection.cs	(revision 10303)
+++ DicomAttributeCollection.cs	(working copy)
@@ -1055,8 +1055,12 @@
             if (value != null && value != DBNull.Value)
             {
                 Type vtype = value.GetType();
-                if (vtype.IsSubclassOf(typeof(DicomSequenceItem)))
+                if (vtype == this[tag].GetType())
                 {
+                    this[tag] = (DicomAttribute)value;
+                }
+                else if (vtype.IsSubclassOf(typeof(DicomSequenceItem)))
+                {
                     DicomAttribute elem = this[tag];
                     elem.AddSequenceItem((DicomSequenceItem)value);
                 }