SOLVED A little problem with fancyhdr `leftmark` in `article` document

I am having a problem with the leftmark command of the fancyhdr package. This is a tex sample

documentclass[a4paper,11pt]{article}

usepackage{fancyhdr}
pagestyle{fancy}
lhead{}
rhead{leftmark}

author{Author}
title{Title}

begin{document}
maketitle

tableofcontents
newpage

section{first section}
First paragraph

section{second section}
Second paragraph

end{document}

This is the output

As you can see, the problem is that latex (compiling with lualatex) print SECOND CHAPTER instead of FIRST CHAPTER, as the leftmark should give the current section in article mode. If i try to use the builtin pagestyle{headings}, changing the document like so:

...

pagestyle{headings}
%usepackage{fancyhdr}
%pagestyle{fancy}
%lhead{}
%rhead{leftmark}

...

then the output is as expected:

What should I try?