Atom.io open file and close last file open

I don't know how to explain this, but I have the following behavior, when I open a file with out make any change and then open another file, this second file open in the same tab where was the first file, so I have to press control + s o make a change in the file, to avoid loose this file when I open another one. How can I open multimple files without make any change in differents tab.

Thanks in advance.