If you open a label filter dialog from the RadPivotFieldList control for a DateTime field and choose the "is between" or "is not between" operator from the combobox, you will notice that the RadDateTimePicker controls used to filter the dates very small. In this case, the empty value placeholder is clipped and if you choose any dates they are clipped too.

To work this around, you can increase the dialog's width when it opens. You can do this with the RoutedDialogEvents.RequestDialog event.

public MainWindow()
{
	InitializeComponent();
	pivotFieldList.AddHandler(RoutedDialogEvents.RequestDialog, new EventHandler<DialogHostingRequestEventArgs>(this.OnDialogHostRequested), true);
}

private void OnDialogHostRequested(object sender, DialogHostingRequestEventArgs e)
{
	var labelDialog = e.DialogInfo.Content as LabelFilterDialog;
	if (labelDialog != null)
	{
		var w = labelDialog.ParentOfType<RadWindow>();
		w.Width = 500;
	}
}