As you have discovered, there is no duplicate file name detection, when uploading a file within a post, and a later upload will replace the earlier one. Implicit in your post is that the same filename can be used in other posts and that seems to be right as well as the general format for URLs of uploaded image files is:
http://myforum.nabble.com/file/postnumber/filename.extI wasn't aware of the second issue, but I am guessing that the assumption in the code is that there is only one dot in the file name, when generating a filename for a thumbnail image (that needs to be available should the app ever be changed to the Gallery or News type). They get stored at:
http://myforum.nabble.com/file/thumb/postnumber/filename.extSo I believe that, currently, the only solution for either issue is to rename your files before upload.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.