Created attachment 116999 [details]
Test case

The PDF gradient generated by following LaTeX document is rendered incorrectly:

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{shadings}

\begin{document}
\begin{tikzpicture}
\shade[shading=color wheel, opacity=.6, shading angle=220] (0,0) circle (1);

\end{tikzpicture}
\end{document}

Okular renders this incorrectly: grid lines and very bad gradient resolution (see screenshots). The grid lines disappear when "shading angle=220" is removed from the source.