Grouping problem in figure vertical alignment of text

Question

I had the same problem as in LINK. The question is about using \endgroup somewhere. If I use the following code

\usepackage[a4paper,hmargin=1in,top=1.2in,bottom=1in]{geometry}
\usepackage{lipsum}
\usepackage{wrapfig} 
\usepackage{pgfplots}
\pgfplotsset{width=10cm,compat=1.9}
\begin{document}
\begingroup
\setlength\intextsep{0pt}
\begin{wrapfigure}{r}{0pt}
\begin{tikzpicture}[scale=0.5]
\draw[step=1cm,very thin] (0,0) grid (13,8);
\end{tikzpicture}
\end{wrapfigure}
\noindent \lipsum[1]
\endgroup
\end{document}

it would look like this picture

However, if I add an empty line after \lipsum[1]

(... like above)
\noindent \lipsum[1]
\endgroup
\end{document}

it would look like this picture

Why is there a difference in the code? If I replace this empty line with \\, \newline or even \hfill \break, none changes. What does this ''empty line'' in grouping mean? Is there other way to fill this empty line to make the code work as in the second picture?