Welcome Soubriquet 8))
I'm going to quote for you what I wrote at CGTalk about his matter:
"Photoshop will always add ?copy? if you?re saving a file with the same name in the same folder, but only when you have more than one layer and use a file format that doesn?t support multiple layers.
You can test this yourself with for example Jpeg as format. Change the format to ?TIFF? in the pull-down menu and you?ll notice that the word ?copy? will disappear again, since TIFF supports multiple layers.
The reason why so many other people never experienced this is because they mostly use (for good reasons) ?Save for Web? which not only has more options for optimization and a preview, but it also doesn?t have the ?copy? problem.
So why was it added? I think it?s because of the following. Certain formats allow you to save multiple layers, PSD is one of them. It?s also possible to save to PSD without using layers, that?s why there?s an option called layers in the ?Save As? window. Turn it off and you?ll notice when you want to save the file with the same name in the same directory that it will add ?copy? to the file name, probably as an extra protection on top of the regular ?Do you want to replace it?? window that you get when you try to save to the same file.
I think Adobe wanted to make sure that users wouldn?t overwrite huge Photoshop files with hundreds if not thousands of layers file by accident. Personally I think they?ve gone too far. Because let?s face it, in order to overwrite a layered PSD file with a version that is not layered, you have to:
a. save to the same folder
b. give the file the same name
c. unselect the ?layers? checkbox
d. ignore the ?Do you want to replace? warning window.
That we see the ?copy? behavior with Jpeg (and not only Jpeg) seems to me like a bug, since no Jpeg can ever have multiple layers.
Don't forget that some bugs take years for Adobe to solve, that is if they want to solve it. A good example is the famous "invisible cursor" on a 50% gray background, it took years before they were willing to solve it in (CS2)."
