A Modeless Dialog Problem

[Calculator]

I am writing a plugin for an iTunes application and trying to pop-up a little dialog box. When I get the word I say

// On dialog creation notification...

            HWND dlg = CreateDialogParam(
                GetModuleHandle(TEXT("Itunesplugin.dll")), 
                MAKEINTRESOURCE(IDD_DIALOG),
                0, &DlgProc, LPARAM(vpd));

And the dialog resource is defined as

IDD_DIALOG DIALOGEX 10, 10, 294, 153, 0
STYLE DS_MODALFRAME | 0x0004 | WS_CAPTION | WS_SYSMENU | WS_VISIBLE | WS_POPUP
CAPTION "Dialog"
FONT 8, "MS Sans Serif", 700, 0 /*FALSE*/
BEGIN

    /* ... Stuff... */

END

As it is a plugin app, I do not know whether iTunes does something like IsDialogMessage or something, but I do know that the presence of my dialog messes up the app, so that it isn't updated and I drag my dialog around and it looks like when you win at the windows solitaire, like this:

http://img.photobucket.com/albums/v2...o1/loooolc.jpg

What is the problem, and how can I fix it?

[Calculator]

Note: This problem exists whether or not the dialog was created in the same or a different thread than the main thread calling the plug-in