Missing \endgroup error for Beamer standalone with subpreambles option [closed]

Question

I am trying to use Martin Scharrer's nifty standalone package to put a Beamer animation into a standalone file. Here is a minimal example that demonstrates the error I am running into. The subfile, creatively named subfile.tex, that I am using is:

\documentclass[beamer]{standalone}

\usepackage{tikz}
\newcommand*{\mytext}{Hello world!}

\begin{document}%
\begin{standaloneframe}{Subfile}
  \begin{tikzpicture}
    \onslide<+->{\draw[red] (0,0) circle (3pt);}
    \onslide<+->{\draw[blue] (1,1) circle (3pt);}
    \onslide<+->{\draw[green] (2,0) circle (3pt);}
    \onslide<+->{\node at (1,2) {\mytext};}
  \end{tikzpicture}
\end{standaloneframe}%
\end{document}

On its own, this subfile compiles as expected.

The main file, named mainfile.tex, that I am using is:

\documentclass{beamer}
\usepackage[subpreambles=true]{standalone}

%\usepackage{tikz}
%\newcommand*{\mytext}{Hello world!}

\begin{document}
\begin{frame}{Main file}
  \input{subfile.tex}
\end{frame}
\end{document}

When I try to compile this main file with pdflatex mainfile.tex, I get an error:

Runaway argument?
%\begin {standaloneframe}{Subfile}\begin {tikzpicture}\onslide <+->{\draw \ETC.
! File ended while scanning use of \sa@@endinput.

When I try a second run of pdflatex mainfile.tex, this runaway argument error disappears, but another error takes its place: Extra }, or forgotten \endgroup. I use X at the prompt to quit compilation after the error. Subsequent runs of pdflatex mainfile.tex continue to give this missing \endgroup error.

I have noticed a few things:

• If I remove the subpreambles=true option and uncomment the two lines of copied preamble (\usepackage{tikz} and \newcommand*{\mytext}{Hello world!}), this modified main file compiles as expected.

• However, if I keep the subpreambles=true option but uncomment the two lines of copied preamble, I get the same error when I try to compile. This suggests that something goes wrong in the subpreambles=true option.

Does anyone know what I am doing wrong here? In his comment below, Martin Scharrer mentions that multiple compilation runs work for him. I'm not sure why I seem to be unable to get multiple compilation runs to work for me.