Good news, I found the solution! While exploring this forum, especially the thread entitled "Where is the latest version of Java3D" I discovered that there was a
1.7.0-final version of Java3D while I had stayed at a
1.7.0-pre1 version. This version fixes the mentioned bug, but also the
parameter in processStimulus(Iterator criteria) of the class Behavior, and other little things.
Thanks for maintaining Java3D!
Jerome