[NTG-context] Strange behaviour with tikz

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 ?