\savebox doesn't work inside tikz foreach loop

Question

I need to process listed content passed to a \foreach loop inside a tikz environment. But \savebox seems not to behave the same as outside tikz.

In particular, the following code:

\documentclass{report}

\usepackage{tikz}

\newsavebox{\aBox}

\newcommand{\withoutTikz}[1]{%
    \foreach \content [count=\i] in {#1} {%
        \savebox{\aBox}{\content}% store content in the box..
        \i : \usebox{\aBox}% use the box

    }%
}

\newcommand{\withinTikz}[1]{%
\tikz{% within tikz..
    \foreach \content [count=\i] in {#1} {%
        \savebox{\aBox}{\content}% store content in the box the same way..
        \node at (0, -.5*\i) {\i : \usebox{\aBox}}; % .. but now it seems empty!
    }%
}
}

\begin{document}

\withoutTikz{a,b,c}

\withinTikz{a,b,c}

\end{document}

produces:

Why? Am I missing anything?
How do I get this aBox content updated on each iteration within the tikz environment?

---

[EDIT:] Problem duplicated there. Based on marmot's answer there, here is how I have solved it :)

\newcommand{\tikzSaveBox}[2]{
     \begin{pgfinterruptpicture}%
     \begin{lrbox}{0\null\global\setbox\csname#1\endcsname}%
     #2
     \end{lrbox}%
     \end{pgfinterruptpicture}
}

\newcommand{\withinTikz}[1]{%
 \tikz{% within tikz..
     \foreach \content [count=\i] in {#1} {%
     \tikzSaveBox{aBox}{\content} % special case within tikz
     \node at (0, -.5*\i) {\i : \usebox{\aBox}}; % .. now it works fine :)
     }%
}
}