I think it's because the file handling on windows is very extension-dependent. They probably assume that a dot marks an extension, and as such treat ".foo" as a

I think it's because the file handling on windows is very extension-dependent. They probably assume that a dot marks an extension, and as such treat ".foo" as a file of type "foo" with no name, which is seen as an error. This is all a clusterfuck honestly, since they rely on extension to figure out how to treat the files, but at the same time hide the extensions from the user by default. I can understand that extensions might look a bit "noisy" but then just gray them a bit to make the rest of the file name stand out, don't hide them completely.