Problem with decorations in a small TikZ picture [closed]

Question

When working on yesterday's update on my answer to the december challenge (a dcorated tree), I encountered a problem: if I choose the picture's dimensions to small, then it fails with

Dimension too large.

Code

\documentclass[tikz, border=2mm]{standalone}
\usetikzlibrary{decorations.markings}

\begin{document}

\newcommand{\XMasPic}[5]%
% x pos, ypos, width, height, draw commands
{   \begin{scope}[shift={(#1,#2)}, x={(#3,0)}, y={(0,#4)}]
        \fill[gray!5] (0,0) rectangle (1,1);
        \draw[clip] (0,0) rectangle (1,1);
        #5
        \draw (0,0) rectangle (1,1);
    \end{scope}
}

\newcommand{\DecoratedTree}[4]%
{ \XMasPic{#1}{#2}{#3}{#4}%
    {   \fill[inner color=blue!40!black, outer color=blue!10!black] (0.02,0.02) rectangle (0.98,0.98);
        \xdef\CuCo{0}
        \draw
        [   yellow,
            bend left=10,
            decoration=
            {   markings,
                mark=between positions 0.01 and 1 step 0.02 with
                {   
                    \pgfmathtruncatemacro{\C}{mod(\CuCo,3)}
                    \fill[inner color=\ifcase\C red\or blue\or yellow\fi, outer color=transparent, opacity=0.2] (0,0) circle (0.015);
                    \fill[inner color=\ifcase\C red\or blue\or yellow\fi, outer color=\ifcase\C red!50\or blue!50\or yellow!50\fi] (0,0) circle (0.005);
                    \pgfmathparse{\CuCo+1}
                    \xdef\CuCo{\pgfmathresult}
                }
            },
            postaction={decorate}] (0.61,0.21) to (0.40,0.265) (0.585,0.325) to (0.43,0.38) (0.56,0.44) to (0.45,0.50) (0.55,0.55) to (0.46,0.61) (0.53,0.665) to (0.475,0.72);
    }
}

\begin{tikzpicture}
    %\DecoratedTree{4}{0}{3.2}{3.2} % fails; 
    \DecoratedTree{0}{0}{3.3}{3.3}
\end{tikzpicture}

\end{document}

Expected Output

The \XMasPic is a wrapper that scales the image to the desired dimensions (width #3 and height #4) and internally provides a coordinate scaling so that all coordinates can be expressed as values bewtween 0 and 1 (see Caramdir's answer to this question)

This error appears to occur due to the small increment in the decoration:

mark=between positions 0.01 and 1 step0.02with {...}

I suspect that the step 0.02 is so small that pgfmath rounds it to zero and therefore never finishes.

Can anyone confirm this is the reason for this error, and ideally recommend a way to get around it?