I'm using SharePoint Foundation 2013, where I have applied all updates and security fixes published by Microsoft.
I'm experiencing this weird problem modifying Excel 2003 (xls) files on Excel 2016: when I click on save button, document seems to be uploaded to SharePoint. On SharePoint I can see the modified date updated, but looking into the file the content is not updated.
I've also versioning enabled and for example, in my case, version 6.0 is the same as the version 7.0 (that is the latest) of the Excel file.
I've googled a lot, but I can find users that have the opposite problem (file updated but modified date not) and not similar problems like mine.
I've no file pending in the Upload center, if it could be related to the issue.