It may happen that document name (especially for certain document types) can contain different information from the expected value set on Form tab. This is probably caused by setting incorrect field which is used for document name within particular document type. One can choose it during document type creating or for preexisting document type by accident anytime else.
You can change it in: Site Manager -> Development -> Document types -> particular_document_type -> Fields. Here is dropdown list called ‘Document name source field’ where you can choose whatever field from actual document type as per your needs. Finally you need to save document itself to change its name to correct one.
Defining a new document type documentation.