When editing a PDF/A document stored in a file cabinet using the Edit & Send function it does not save the changes in DocuWare.
Editing must be performed using a PDF Editor such as Adobe Acrobat.
The following changes must be made in the editor in order to enable the "Save" function:
1. Open Adobe Acrobat (or equivalent) and select  > Edit > Preferences > Categories > Documents
2. Change PDF/A View Mode from Only for PDF/A documents to View documents in PDF/A mode: Never
3. Close Adobe > Edit PDF > Save changes

PDF/A Edit - View Mode Changes