[ModernDialog][MessageBoxResult] Cancel Button on second windows

Hi,

I'm using the ModernDialog that contains a UserControl, it has a custom button:

Button customButtonClose = new Button() { Content = "Close" };
customButtonClose.Click += (ss, ee) =>
{
	CheckPendingChanges();
	dialog.Close();
};
dialog.Buttons = new Button[] { customButtonSave, customButtonClose };

In CheckPendingChanges():

var rsltDialog = Utils.ShowMessageYesNoClose("Are there a pending changes, save?");

if (rsltDialog == MessageBoxResult.Yes)
{
	result = customFunction();
}

where Utils.ShowMessageYesNoClose() is:

public static MessageBoxResult ShowMessageYesNoClose(string text)
{
	var dlg = new ModernDialog
	{
		Title = (string)Application.Current.FindResource("mdAppTitle"),
		Content = new BBCodeBlock { BBCode = text, Margin = new Thickness(0, 0, 0, 8) },
		MinHeight = 0,
		MinWidth = 0,
		MaxHeight = 480,
		MaxWidth = 640,
	};
	dlg.YesButton.Content = (string)Application.Current.FindResource("msgBoxResultYes");
	dlg.NoButton.Content = (string)Application.Current.FindResource("msgBoxResultNo");
	dlg.Buttons = new[] { dlg.YesButton, dlg.NoButton, customCancelClose, dlg.CancelButton };

	dlg.ShowDialog();

	return dlg.MessageBoxResult;
}

I have this problem: when I click on CancelButton, the two windows are closing together, but I would close only second window, the one with the application.

Where is the error?