PDF gradients are incorrectly rendered in Okular.


Reproducible: Always

Steps to Reproduce:
When rendering the PDF file generated by pdflatex from this source:

\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}

Actual Results:  
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.

Expected Results:  
The gradient should render smoothly (see screenshots)

IIRC, I reported a bug about this to qpdfview, which didn't show the grid lines as okular does, but did show a squar texture pattern, albeit interpolated.