Think i found an issue, don't know if it's been submitted before.
You can open the same document multiple times. And if you work on one of those documents, let's say all day and you keep saving it over and over again, just to be sure you won't lose any work. The instance you close it and have other older versions open you may end up losing all your work.
When you exit the app (using the top right X sign) the app will close and save the document. (there will be no save changes dialog, it will just force shut down and save the document)
So when you then close your older versions, it will overwrite your changes
But how I managed to open the same file more then once is beyond me, been trying to replicate it.