Windows Vista: Surprising Feature

We have Windows Vista on our new computer. We have been using Windows XP all this time and have been quite satisfied with it. But the new system had Vista preinstalled on it, and we had to take it. I found a new surpsising feature on it. I had downloaded some large files and taken their back-up on my external hard disk. Two files were incompletely downloaded, and I downloaded them after 2 days. Then I connected my external hard disk to take back-up, and started looking for the downloaded files. When I found them and went to the folder on the external hard disk containing the previous files, I found these two files already there. The files on both internal and external hard disks had the same date and time stamp, and the same size. They were identical. I was foxed. The files had transferred themselves to my external hard disk. I thought about it quite a lot, and finally concluded that Windows Vista had understood that it was my practice to transfer downloaded files to the external hard disk, and done that by itself. It was something like a macro written by one would have done. I did not find such a feature of the Vista on Internet search. If it is a planned feature, I congratulate Microsoft. If it is accidental, I congratulate whoever is responsible for that accident.