Overlay steps in two columns

Question

I have the following slide:

\documentclass[beamer]{beamerswitch}
\usetheme{metropolis}
\beamerdefaultoverlayspecification{<+->}

\begin{document}
\begin{frame}\frametitle{My title}

  \begin{columns}[t]
    \begin{column}{0.49\textwidth}
      \begin{block}{Left side}
        \begin{itemize}
        \item First item;
        \item Second item;
        \end{itemize}
      \end{block}
    \end{column}

    \begin{column}{0.49\textwidth}
      \begin{block}{Right side}
        \begin{itemize}
        \item First item;
        \item Second item;
        \end{itemize}
      \end{block}
    \end{column}
  \end{columns}
\end{frame}
\end{document}

When I compile it, I get 9 pages. On slides 1-2, only the title appears. "Left side" appears on slide 3, and "Right side" appears on slide 7.

What should I change so that "Left side" appears on slide 1 already and there are no extra steps on slide 2 and 6? I would like to keep the default overlay specification for the document.

EDIT: By trial and error, I found this solution:

\documentclass[beamer]{beamerswitch}
\usetheme{metropolis}
\beamerdefaultoverlayspecification{<+->}

\begin{document}
\begin{frame}\frametitle{My title}
\beamerdefaultoverlayspecification{} %switch off for this slide

  \begin{columns}[t]
    \begin{column}{0.49\textwidth}
      \begin{block}{Left side}
        \begin{itemize}[<+(1)->]
        \item First item;
        \item Second item;
        \end{itemize}
      \end{block}
    \end{column}

    \begin{column}{0.49\textwidth}
      \begin{block}{\uncover<4->{Right side}}
        \begin{itemize}[<+(2)->]
        \item First item;
        \item Second item;
        \end{itemize}
      \end{block}
    \end{column}
  \end{columns}
\end{frame}
\end{document}

I don't understand why it does what it does. If \beamerdefaultoverlayspecification{<+->} is in effect, beamer poses twice after printing the title. Why? It seems something is changing the value of the beamerpauses counter, but if I understand the manual correctly, neither the column nor the block environment is supposed to do that. So what's injecting all these pauses?

Answer 1

Next try. [<+(1)->]

\documentclass[beamer]{beamerswitch}
\usetheme{metropolis}
%\beamerdefaultoverlayspecification{<+->}

\begin{document}
\begin{frame}\frametitle{My title}

  \begin{columns}[t]
    \begin{column}{0.49\textwidth}
      \begin{block}{Left side}
        \begin{itemize}[<+(1)->]
        \item First item;
        \item Second item;
        \end{itemize}
      \end{block}
    \end{column}

    \begin{column}{0.49\textwidth}
      \begin{block}{Right side}
        \begin{itemize}[<+(1)->]
        \item First item;
        \item Second item;
        \end{itemize}
      \end{block}
    \end{column}
  \end{columns}
\end{frame}
\end{document}

Answer 2

Unfortunately I can not say anything to why this happens, but the following fixes the issue for me through patching the columns and column environments with etoolbox:

\usepackage{etoolbox}
% when using columns we get two empty pages before itemize without this, 
% when using \beamerdefaultoverlayspecification{<+->} 
\preto\columns{\addtocounter{beamerpauses}{-1}}
\preto\column{\addtocounter{beamerpauses}{-1}}

After that no empty pages appear before the list, and the overlaying runs through both columns like expected.