...and I got another experience.

If I only put Application.DisplayFormulaBar = True in the CommandButton then the formulabar won't show, when closing the workbook/application with the closing X (upper right). That should be obviously.
If I only put Application.DisplayFormulaBar = True in the closing event then the formularbar won't show, when closing the workbook from the button. That I don't understand.

So, put Application.DisplayFormulaBar = True in both will do it!