We didn't do anything special to not make it work under Microsoft Word 2016.
Sure hope not, that would be one epic troll.
Maybe this has something to do with one of the converter libraries you are using on the back-end? I saw that for spreadsheets you are using OnlyOffice. Is this also for the Rich Text editor? If you are using OO as your back-end then I'm sure I'm not the only one who is facing this issue.
I would love to file an issue with Microsoft but it would help to know exactly what the workflow is to reproduce the scenario.