[xwiki-users] Excel file attachment problems

Hi all, I have my XWiki 5.1 deployment set up to store attachments in the file system (not database). If for e.g. I upload a docx file as an attachment and download it, it all works fine. If I upload a Microsoft Excel file (xlsx, xlsb, xlsm, etc.) it attaches fine, but opening presents a few strange problems. If it is a plain xlsx file, clicking open instead of save when downloading the attachment prompts me to enter a server password. If I click save, it downloads and I can open it fine. For xlsb and xlsm files, the attached file is served as a .zip file... I have no clue why. It's like this in any browser I try. I'm not sure where the problem lies. Any ideas? Thanks.