I would expect that you’d want the model to be dynamic, that is, responding to collisions. (See this page, for reference: Bullet Hello World — Panda3D Manual ). Try setting that flag to “True”, see whether that helps.
It finally works! Thanks @ Thaumaturge!
I also had to remove flattenLight line because it messed geometries positions and so the model was created with serious problems (all pieces were flying in a crazy dance… 
). I read here that flattenLight is indicated to static objects (without transformation later), not my case at all!