Ugly artifacts with pgf-blur and beamer (and poppler)

Question

I am trying to add blur shadows to a beamer presentation using the pgf-blur package. Here is a minimal working example:

\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{shadows.blur}

\begin{document}

\begin{frame}
\begin{tikzpicture}
\node[minimum height=1cm, minimum width=3cm,
  rounded corners, fill=red!30, blur shadow] {};
\end{tikzpicture}
\end{frame}

\end{document}

Unfortunately, when I try to present my slides using any of the poppler-based renderers (like xpdf, evince, okular, impressive), I get an extremely ugly artifact at the border and especially corners. Here is what it looks like:

Interestingly, the problem goes away if I do the same thing in a \documentclass{article}. Here is a screenshot of the same image without beamer:

Because the problem does not happen with mupdf, this may actually just be a bug in libpoppler. However, libpoppler is so prevalent that I need to find a way to work around it. The fact that the bug goes away without beamer gives me some hope there is a way around this, but I have no idea what beamer might be doing to cause the artifact. I'd also be happy with an alternative to pgf-blur, if there is one.

Answer 1

Here is a workaround:

\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{shadows.blur}
\tikzset{
  my blur shadow layer/.style={
    preaction={fill=black,fill opacity=.025,transform canvas={xshift=#1,yshift=-1*#1}},
  },
  my blur shadow/.style={
    my blur shadow layer/.list={.3pt,.6pt,...,2.7pt},
  },
}
\begin{document}

\begin{frame}
\begin{tikzpicture}
\node[minimum height=1cm, minimum width=3cm,
  rounded corners, fill=red!30,
  blur shadow,
  ] {};
\node[minimum height=1cm, minimum width=3cm,
  rounded corners, fill=orange!30,
  my blur shadow,
  ] at (0, -1.2){};
\end{tikzpicture}
\end{frame}

\end{document}