On a mac you can you have duplicate file name in a folder that does not sound right, Does Apple have a versioning option, Photoshop does not. Why would the original file be copied as a newer file? Photoshop would not copy the originals as new file before saving over the original. Save has no parameters. No Name is passed to save no file format is passed to save, no Path is passed to save. There is just save. Now if the file opened was a Jpeg and you add a layer and did not flatten and you use Save. Save will switch to Save As to give you an opportunity to save your layers and offer PSD as the file type switch from jpg.
Apple should be using a Unix type file system. Which supports Mix case file names Windows really does not. For on windows there the can only file with the name X. Be a file the name X or x thet can not be a file X and a file x in a folder. I use Windows Does Mac OS File systems support a versioning option or attribute.
Thank you JJMack,
It was an option on the Mac under system preferences that I didn't check. I didn't realize I needed to check that box.
All good now thanks for your help!
For anyone in future it's System Preferences>General>Check the box that says Ask to keep changes when closing document