Mysterious summing: when calculator 's \ADD macro adds too much inside a table

Background: In my previous question, Robert Fuster taught me how to define a global variable using calculator package.

I want to define a "counter" that also works with non-integers. I thus defined an \addtocounter-like macro as following (assuming that \mySum and \whatIAdd have been previously defined):

\ADD{\whatIAdd}{\mySum}{\mySum}
\GLOBALCOPY{\mySum}{\mySum}

My macro works well in normal text mode (see below). However, if I use it inside a table, it "mysteriously" does each addition once before plotting the table. Even if I reset it at the beginning, \mySum equals the sum of each \whatIAdd in my table.

Question: where does this artefact comes from, and how to remove it?

\documentclass{scrartcl}
    \usepackage{calculator}
    \usepackage{array,tabulary,booktabs}

    %% Macro definition %%
    \newenvironment{mytable}
    {
        \GLOBALCOPY{0}{\mySum}
        \texttt{mySum} equal \mySum

        \tabulary{\linewidth}{CC}
        \toprule
        \textbf{A}&\textbf{$\Sigma$ A}\\
        \midrule
    }{
        \endtabulary
    }


    \newcommand{\makeline}[1]
    {%
        \COPY{#1}{\whatIAdd}
        \ADD{\whatIAdd}{\mySum}{\mySum}
        \GLOBALCOPY{\mySum}{\mySum}
        %
        \whatIAdd & \mySum\\
    }

    \newcommand{\resetMySum}{\GLOBALCOPY{0}{\mySum}\noindent I've reseted \texttt{mySum}. It's value is now \mySum .\newline}
    \newcommand{\addMySum}[1]
    {
        \COPY{#1}{\whatIAdd}
        \ADD{\whatIAdd}{\mySum}{\mySum}
        \GLOBALCOPY{\mySum}{\mySum}
        %
        \noindent I added \whatIAdd{} to \texttt{mySum}. It's value is now \mySum .\newline
    }

\begin{document}
    \begin{minipage}{.25\textwidth}
        \begin{mytable}
            \makeline{0}
            \makeline{1}
            \makeline{42}
            \bottomrule
        \end{mytable}
    \end{minipage}
    \begin{minipage}{.75\textwidth}
        \resetMySum
        \addMySum{0}
        \addMySum{1}
        \addMySum{42}
    \end{minipage}
\end{document}