exam/wrapfigure: Text doesn't wrap around the figure

Question

For the following MWE, why is the first image overlayed with the text when using \lipsum instead of pasting dummy text?

And how to fix the other two images to be placed properly next to their respective texts?

\documentclass{exam}
\usepackage{adjustbox,wrapfig,lipsum}

\newenvironment{mywrapfigure}
{%
    \setlength{\columnsep}{15pt}%
    \wrapfloat{figure}%
}
{\endwrapfloat}

\begin{document}

    \begin{mywrapfigure}{r}{0.3\linewidth}
        \centering
        \includegraphics[width=\linewidth]{example-image-a}
    \end{mywrapfigure}

    \lipsum[1]

    \bigskip
    \begin{questions}
        \question

        \begin{mywrapfigure}{r}{0.3\linewidth}
            \includegraphics[width=\linewidth]{example-image-b}
        \end{mywrapfigure}

        \lipsum[1]

        \bigskip
        \begin{parts}

            \part[4]

            \begin{mywrapfigure}{r}{0.3\linewidth}
                \includegraphics[width=\linewidth]{example-image-c}
            \end{mywrapfigure}

            \lipsum[1]

        \end{parts}

    \end{questions}
\end{document}