Listbox - Show Only The First Items As Selected

I have a list box which is populated using a dictioanry. When I iterate throught the selected items using the following code, it always show only the first items as selected - even if the first item is not selected. Have you ever encountered this scenario? This problem occurs when I use dictionary for binding. On the other hand a generic list works fine.

private void PopulateListBox2()
{
List<string> subjectList = new List<string>();
subjectList.Add("Maths");
subjectList.Add("Science");
ListBox1.DataSource = subjectList;
ListBox1.DataBind();
}

Even it will work fine, if the values are unique. But in my scenario, the values are same; only key varies. The following works

private void PopulateListBox5()
{
Dictionary<string, string> resultDictionary = new Dictionary<string, string>();
resultDictionary.Add("Maths", "Lijo1");
resultDictionary.Add("Science", "Lijo2");
ListBox1.DataValueField = "Value";
ListBox1.DataTextField = "Key";
ListBox1.DataSource = resultDictionary;
ListBox1.DataBind();
}

The following code has the problem......................