ListItemCollection.AddRange sets selection to the first item

I have a custom DropDownList derived from System.Web.UI.WebControls.DropDownList.
And I've noticed that after populating data using
ListItemCollection.AddRange Method,
the DropDownList.SelectedIndex Property becomes set to 0 from -1.

I consider this as an unexpected behavior and have to change it back to -1- unselected.

            Items.Clear();

            Debug.Assert(SelectedIndex == -1);

            Items.AddRange(cachedItems);

            Debug.Assert(SelectedIndex == 0);//is it correct?

«August»
SunMonTueWedThuFriSat
2930311234
567891011
12131415161718
19202122232425
2627282930311
2345678