I think that the problems you are experiencing are due to how you are editing the forms. When you are editing a form that was not created with Form Builder like the login form from Security Assist the field names will be used for the labels. Once you make these changes though in the Form Builder you will be able to retain them so long as you editing from the edit form interface.
The edit form option appears in the property inspector, you must select the CSS Form Builder tag that appears around the form, it is a bluish-green color. When this is selected you will have the options to edit the form, edit the design, or just the contents directly from the property inspector.
CSS Form Builder is designed so that you can save the various parts of the form and the form as a whole so that you don't need to redo any of the editing that has already been done.