Image shifts when removing percent (%) signs with standalone class

Question

I have occasionally observed that some LaTeX macros behave differently with and without end-of-line comments. My understanding of this is that a macro may leave a space on the stack that for some reason is removed if the macro is ended with a percent sign. I have never quite understood why this happens so I've slowly fallen into the habit of ending all "function calls" in LaTeX with %. In the present case, I discovered that \pstScalePoints and \newpsstyle behaves just like that and took the effort to isolate the problem into the following MWE:

\documentclass{standalone}
\usepackage{pstricks}
\usepackage{pstricks-add}
\usepackage{pst-plot}
\listfiles
\begin{document}
\readdata{\mytable}{table.txt}  
\pstScalePoints(1.0,1.0){1.0 div}{1.0 div}%  <-- NB!
\newpsstyle{legendstyle}{fillstyle=solid}%   <-- NB!
\begin{psgraph}(0,0)(0,0)(1,1){1cm}{1cm}
\listplot{\mytable}
\end{psgraph}
\end{document}

Problem: The output changes if the two end-of-line % signs are removed. My suspicion is that the macros leave behind a space on the stack, but I do not know how to correct it - other than stubbornly adding % to all the macro endings!

The contents of file table.txt is:

0.0, 0.00
0.2, 0.04
0.4, 0.16
0.6, 0.36
0.8, 0.64
1.0, 1.00

I halfway expect that the problem depends on which packages I am using so I therefore include the output from \listfiles:

pstricks.sty      2013/12/12 v0.60
pstricks.tex      2014/10/25 v2.60
pst-xkey.tex      2005/11/25 v1.6
pst-fp.tex        2014/10/25 v2.60
pstricks-add.sty  2010/02/11 v.0.14
pst-plot.sty      2011/04/13
pst-xkey.sty      2005/11/25 v1.6
pst-plot.tex      2014/08/23 1.70
pst-node.sty      2010/04/22
pst-node.tex      2014/08/04 1.35
pstricks-add.tex  2014/12/08 v3.77
pstricks-add.cfg  2005/01/10 v0.1

Finally, I've attached two pictures illustrating the problem:

1. With end-of-line comment
   
   _{(source: ntnu.no)}

2. Without end-of-line comment
   
   _{(source: ntnu.no)}

Answer 1

This is a specific problem of standalone. You can look at What is the use of percent signs (%) at the end of lines? for understanding what follows.

By default, standalone typesets the text in the document environment in a horizontal box (\mbox, essentially), for later cropping.

In a horizontal box, spaces are significant, so the end-of-lines must be hidden with % lest they're converted into spaces.

In a normal document, say with \documentclass article`, you wouldn't see those spaces, because they are seen when TeX has not yet started a paragraph.

So

\documentclass{standalone}
\usepackage{pstricks}
\usepackage{pstricks-add}
\usepackage{pst-plot}
\begin{document}
\readdata{\mytable}{table.txt}%  <-- NB!
\pstScalePoints(1.0,1.0){1.0 div}{1.0 div}%  <-- NB!
\newpsstyle{legendstyle}{fillstyle=solid}%   <-- NB!
\begin{psgraph}(0,0)(0,0)(1,1){1cm}{1cm}
\listplot{\mytable}
\end{psgraph}
\end{document}

On the other hand,

\documentclass{article}
\usepackage{pstricks}
\usepackage{pstricks-add}
\usepackage{pst-plot}
\begin{document}

\readdata{\mytable}{table.txt}  
\pstScalePoints(1.0,1.0){1.0 div}{1.0 div}
\newpsstyle{legendstyle}{fillstyle=solid}

\begin{psgraph}(0,0)(0,0)(1,1){1cm}{1cm}
\listplot{\mytable}
\end{psgraph}

\end{document}

needs no % because the paragraph starts with \begin{psgraph}.

If you find yourself doing many of this % additions, you can consider adding something to your document:

\documentclass[varwidth]{standalone}
\usepackage{pstricks}
\usepackage{pstricks-add}
\usepackage{pst-plot}

\newcommand{\startsetup}{%
  \chardef\oldendlinechar\endlinechar
  \endlinechar=-1
}
\newcommand{\stopsetup}{\endlinechar=\oldendlinechar}

\begin{document}

\startsetup
\readdata{\mytable}{table.txt}
\pstScalePoints(1.0,1.0){1.0 div}{1.0 div}
\newpsstyle{legendstyle}{fillstyle=solid}
\stopsetup

\begin{psgraph}(0,0)(0,0)(1,1){1cm}{1cm}
\listplot{\mytable}
\end{psgraph}
\end{document}