decoded to 0x00A0?

I want to export a GridView to a text file.  But the original space in database will be rendered as   in inGridView, then become 0x00A0 after being decoded using HttpUtility.HtmlDecode() method.  This is illustrated by the following code.
 
string originalString = " "; // space
string webString =
HttpUtility.HtmlEncode(originalString); //  
string actual = HttpUtility.HtmlDecode(webString); // 0x00A0
string expected = webString.Replace(" ", " "); // space
Is there any way to get back the original space?  I guess this is because .NET string is ...