Item is misplaced using overlay and `Copenhagen` theme

Question

Please consider this MWE:

\documentclass{beamer}
\makeatletter
\newcommand*{\overlaynumber}{\number\beamer@slideinframe}
\makeatother
\usetheme{Copenhagen}
\begin{document}
\begin{frame}
    \begin{block}{}
        Text
        \begin{onlyenv}<1-2>
            \begin{enumerate}
                \setcounter{enumi}{1}
                \item Text
                \begin{columns}[T]
                    \begin{column}{.5\linewidth}
                        \begin{itemize}
                            \item $n=0$
                        \end{itemize}
                    \end{column}
                    \begin{column}{.5\linewidth}
                        \begin{itemize}
                            \item $n=1$
                        \end{itemize}
                    \end{column}
                \end{columns}
            \end{enumerate}
        \end{onlyenv}
    \begin{onlyenv}&lt;3-4&gt;
        \begin{enumerate}
            \setcounter{enumi}{2}
            \item PROBLEM WITH THIS ENUMERATE LABEL
            \begin{itemize}
                \item Text here
                \item More text here
            \end{itemize}
        \end{enumerate}
    \end{onlyenv}
\end{block}

\end{frame}
\end{document}

As you can see, the third item is misplaced (the same happens with itemize environment).

I tried several things, but one thing came to my mind: What happens if we delete \usetheme{Copenhagen}? The item is well placed.

However I need that theme, and also the enumerate environments have to be separated in order to use onlyenv.

Perhaps adding \usepackage{enumitem} and moving that item to the right? I came across this excellent answer: "Don't use enumitem with beamer."

How can we solve this issue using the theme and preserving overlays?

Answer 1

You can avoid the problem by placing your columns after the itemize environment instead of at the end of it:

\documentclass{beamer}
\makeatletter
\newcommand*{\overlaynumber}{\number\beamer@slideinframe}
\makeatother
\usetheme{Copenhagen}
\begin{document}
\begin{frame}
    \begin{block}{}
        Text
        \begin{onlyenv}<1-2>
            \begin{enumerate}
                \setcounter{enumi}{1}
                \item Text
            \end{enumerate}
            \begin{columns}[T,onlytextwidth]
                \begin{column}{.5\linewidth}
                    \begin{itemize}
                        \item $n=0$
                    \end{itemize}
                \end{column}
                \begin{column}{.5\linewidth}
                    \begin{itemize}
                        \item $n=1$
                    \end{itemize}
                \end{column}
            \end{columns}
        \end{onlyenv}
    \begin{onlyenv}&lt;3-4&gt;
        \begin{enumerate}
            \setcounter{enumi}{2}
            \item PROBLEM WITH THIS ENUMERATE LABEL
            \begin{itemize}
                \item Text here
                \item More text here
            \end{itemize}
        \end{enumerate}
    \end{onlyenv}
\end{block}

\end{frame}
\end{document}