Duplicate of a form field read only

I have a form where I have a read write text field. The same content of the field must appear as read only in another text field. So I created two text field with same property, one read only and one read write.
Unfortunately they are both read only. It seems that the last one state wins.
What can I do?

This is not supported. The best way to handle such cases will be to convert the Form to TemplateForm and use some non-input element (like Label for example) to present the read-only part: