使用比例选项时 TikZ 图片中的伪影

Question

使用 pdflatex 版本 3.1415926-2.4-1.40.13 (TeX Live 2012/W32TeX) 编译下面的示例代码时，我在缩小版的 tikzpicture 中观察到一个瑕疵（从对象起点开始的水平线）。如能提供任何有关如何修复此问题的帮助，我将不胜感激。

\documentclass{article}
\usepackage{tikz}

\begin{document}

  \def\myFig{
      +(0,0) to [out=90,in=270]  +(0,1)
             to [out=90,in=270]  +(1,3)
             to [out=90,in=270]  +(-0.3,1)
             to [out=90,in=180]  +(1,1)
             to [out=0,in=90]    +(1,-1)
             to [out=270,in=90]  +(-0.3,-1)
             to [out=270,in=90]  +(1,-3)
             to [out=270,in=90]  +(0,-1)
             to [out=270,in=0]   +(-0.3,-0.3)
             to [out=180,in=0]   +(-2.8,0)
             to [out=180,in=270] +(-0.3,0.3)
             -- cycle;
  } 

  scale=1: figure looks ok

  \begin{tikzpicture}[scale=1]
    \draw[step=1,lightgray] (-5,0) grid (5,10);
    \draw[gray,thick,fill=gray!10] (-4.2,2.5) \myFig;
    \draw[thick,fill=gray!40,rotate=-18] (0.7,1.1) \myFig;
  \end{tikzpicture}

  \vspace{1cm}
  scale smaller than 1:  figure contains additional lines

  \begin{tikzpicture}[scale=0.4]
    \draw[step=1,lightgray] (-5,0) grid (5,10);
    \draw[gray,thick,fill=gray!10] (-4.2,2.5) \myFig;
    \draw[thick,fill=gray!40,rotate=-18] (0.7,1.1) \myFig;
  \end{tikzpicture}

\end{document}