It seems that moving an attachment to a page that has an attachment with the same name loses the old one ...
I have just moved SmiliesPlugin.zip from SmiliesPluginDev to SmiliesPlugin and the old version of the package seems to be disappeared.
-- AndreaSterbini - 19 May 2002
Stands to reason that if you move a file from one directory to a directory that contains a file of the same name its going to get over written.
Possible Solutions that I can see:
Come up with a warning convention letting the user know if this is about to happen. and require confirmation
Detect when file already exists. and propose a _# to the new file name
Detect when file already exists, and upload with the same file name but with a new (higher) version number (maybe with the option to overwrite (delete) the old verion if disk space is an issue.