As the P11D Organiser has been downloaded before setup.exe will exist in your server cache. The reason for this is that caching improves general performance.
There are two ways to get the file you need. One would be to clear the file from the cache but this would be something only an administrator would normally do. The other would be to email us and we will supply a setup with a different filename that you can download from a different area. Because we call our installation file setup.exe, a web browser will never tell what version it is at all.