Beamer: "No section" section; erratic behavior of "\section*{}"

Question

I have updated to Ubuntu 18.04 and I am using TexLive 2017 from the repositories.

In my Beamer presentations, I have always used \section*{} before the last slides corresponding to acknowledgements, thank you to the audience, etc. Like this, those slides do not correspond to any section. This is detailed in this question.

However, now that command does not produce the desired effect. In the MWE below, the circles corresponding to the navigation on top of the slides should not be filled for the "no section" slides, but now they are filled and they screw up the navigation (which should direct to the "My Section" slides when clicking in the circles...).

Why does the \section*{} command not work correctly now? Is it deprecated now? What should be the correct way to obtain the effect it used to have? Thanks!

\documentclass{beamer}

\mode<presentation> {
    \usetheme{Singapore}
    \usecolortheme{orchid}
}

\begin{document}

\begin{frame}[plain]
\titlepage % Print the title page as the first slide
\end{frame}

\section{My Section}
\begin{frame}
My Section slide 1
\end{frame}

\begin{frame}
My Section slide 2
\end{frame}

\section*{} %"no section" section
\begin{frame}
No section slide 1
\end{frame}

\begin{frame}
No section slide 2
\end{frame}

\end{document}