Customer today reported this issue.
When she was dragging and dropping an attachment from an email in Outlook 2016 Mac (OS is 10.11.5) to her desktop, instead of it downloading the attachment in the email it downloaded a completely different document.
After some testing I determined that what it is doing is downloading the previously downloaded attachment. So, if I drag and drop Attachment B, it downloads Attachment A, and then if I drag and drop Attachment C, it downloads Attachment B.
This is ONLY for dragging and dropping, not for opening or saving to desktop (both are the suggested workarounds for her).
Any ideas?