This is due to the editing, let me explain the situation.

When you create document via the API and specify a sender contact that *does not exist* as a contact in your company, the address you specified is stored as text.

The alternative is specifying a sender contact, that *does* exist as a contact in your company. In this case, the address is not stored as text, but the document is linked to the contact that you have created in your company, it pulls the address from there when creating the PDF.

Now, the problem you are experiencing, is that a contact that does not exist is being specified, so the address is stored as text, but then the document is edited. When editing a document in the MakeLeaps UI, we don’t allow entering the address as text, and only allow the linking them via contacts, when this is saved, it being linked to no contact and so the address previously entered via the API is being overwritten.