Paint stores subsequent file changes in the Unnamed.bmp

First, I saved my picture in Blizz.bmp (1.bmp and 2.bmp). After that I added the changes and pressed Save item (3.bmp). Paint created Unnamed.bmp file in the same directory and added changes into it (4.bmp). So, Blizz.bmp didn't change. All further changes were made to Unnamed.bmp (5.bmp)