Can't click in dialog within preference dialog.

[Paul Warren <pdw ferret lmh ox ac uk>]

I'm trying to add a button to a preferences dialog that causes a second
dialog to appear, so I connect the "clicked" signal from the button to a
callback:

static void callback (...)
{
	GnomeDialog * dialog;
        dialog = GNOME_DIALOG(gnome_message_box_new ( "foo", 
                    GNOME_MESSAGE_BOX_QUESTION,
                    GNOME_STOCK_BUTTON_YES,
                    GNOME_STOCK_BUTTON_NO,
                    NULL));
	gnome_dialog_run_and_close(dialog);
}

When I do this, the message box comes up fine but I can't click on the
buttons - when I move the mouse over them they highlight, and when I
click they cease to be highlighted, but they do not get depressed.  The
keyboard input still works fine, though.

This is only a problem while the (non-modal) preferences dialog is
visible.  What am I missing?

cheers,

Paul