Override name of zip file doesn't work with overloaded AddFile method


I am adding files from various locations to a zip file. These files can potentially have the same name, so I am trying to version the those (adding (1), (2), etc to the name), but only within the zip file.
I am also specifying the path hierarchy within the zip file.
So, for example:

using (ZipFile zip = new ZipFile())
            foreach (FileCollection dir in dirs)
                var zipPath = path1 + "/" + path2 + "/";
                foreach (FileObject file in files)
                            If (isDuplicated(file))
                                var newName = file.Filename + "(1)";
                            zip.AddFile(file.FullPath, zipPath).FileName = newName;
This doesn't work. I get an exception saying "An item with the same key has already been added."

If I remove the zipPath when calling the AddFile method, like so:

zip.AddFile(file.FullPath).FileName = newName;

...everything works fine.
This, it seems like the FileName setter is not working whenever the AddFile overload method is used.