[NTG-context] Strange behaviour with tikz

[Eric DÉTREZ]

Hello again

I don't understand a strange thing.

Patterns in tikz become black in some case.

Here is a minimal example :
***************************************
\usemodule[tikz]
\usetikzlibrary[patterns]
\starttext

blabla

\chapter {blabla}

\starttikzpicture
\draw [pattern=north west lines](0,0) rectangle +(1,2);
\stoptikzpicture

\stoptext
*************************************

Without any text before the chapter or without the chapter command I  
see the patterns.
With these commands I just see a black rectangle.

Can I get my patterns back ?