Why are my pages indented differently [duplicate]

I have written a test document to illustrate the strange behaviour I have encountered. When I compile the code, it indents the paragraph on the first page differently from the second paragraph but when I skip to the third page, the indentation matches the first page. Please help. My code is below:

\documentclass[11pt,twoside]{article}
\usepackage{apacite}
\usepackage{graphicx}
\usepackage{subcaption}
\setlength{\parindent}{0pt}
\begin{document}
%\nocite{*} % use if we want to see a list of all references
%\input{title_page}
% \input{abstract}
% \input{table_of_contents}
% \input{introduction}
\section{dude}

\par sdfdsflsgssdfsd \newpage
\par sfsdfsfsfsdfsfsd \newpage
\par sfsdfsdfsfsdfsdfs \newpage

%\input{background}
% \input{research_questions}
% \input{approach}
% \input{related_work}
% \input{thesis_outline}
% \input{project_requirements}
% \input{timeline}
%\input{references}

\end{document}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% End:


Here is a link to the document that gets produced:

marked as duplicate by David Carlisle, user36296, Zarko, user31729, egreg formatting StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Feb 9 '17 at 10:37

Your problem is the use of the twoside class option. It is no problem of indentation, but of margins. So the problem disappears by removing this class option. If you want a two-sided document then this is normal.