It keeps the original string internally, for example, the following code:

    Uri u = new Uri("http://www.example.com/path?var=value%2fvalue");
    Console.WriteLine(u.OriginalString);

will display

http://www.example.com/path?var=value%2fvalue

EDIT: I have update the code found in the Connect Link Workaround for recent .NET versions. Here it is:

// System.UriSyntaxFlags is internal, so let's duplicate the flag privately
private const int UnEscapeDotsAndSlashes = 0x2000000;
private const int SimpleUserSyntax = 0x20000;

public static void LeaveDotsAndSlashesEscaped(Uri uri)
{
    if (uri == null)
        throw new ArgumentNullException("uri");

    FieldInfo fieldInfo = uri.GetType().GetField("m_Syntax", BindingFlags.Instance | BindingFlags.NonPublic);
    if (fieldInfo == null)
        throw new MissingFieldException("'m_Syntax' field not found");

    object uriParser = fieldInfo.GetValue(uri);
    fieldInfo = typeof(UriParser).GetField("m_Flags", BindingFlags.Instance | BindingFlags.NonPublic);
    if (fieldInfo == null)
        throw new MissingFieldException("'m_Flags' field not found");

    object uriSyntaxFlags = fieldInfo.GetValue(uriParser);

    // Clear the flag that we don't want
    uriSyntaxFlags = (int)uriSyntaxFlags & ~UnEscapeDotsAndSlashes;
    uriSyntaxFlags = (int)uriSyntaxFlags & ~SimpleUserSyntax;
    fieldInfo.SetValue(uriParser, uriSyntaxFlags);
}

Of course, it's a hack, so you should use it at your own risks :-)