Doesn't show configuration dialog in modal mode

[knowis1972]

Hello!
I'm exploring NTwain project, WPF samle. There is the call
DsmWinNew(origin, destination, DataGroups.Control, DataArgumentType.UserInterface, msg, data);
where data is
[StructLayout(LayoutKind.Sequential, Pack = 2)]
partial class TWUserInterface
{
TW_BOOL _showUI;
TW_BOOL _modalUI;
TW_HANDLE _hParent;
}

and
TW_BOOL = System.UInt16;
and _showUI = 1 and _modalUI = 1 and _hParent is actual window handle

and DsmWinNew defined as
[DllImport("twaindsm.dll", EntryPoint = "DSM_Entry")]
public static extern ReturnCode DsmWinNew(
[In, Out]TWIdentity origin,
[In, Out]TWIdentity destination,
DataGroups dg,
DataArgumentType dat,
Message msg,
[In, Out]TWCieColor data);

Unfortunately dialog doesn't shows in modal mode