OMG Thanks it's working so fu**ing well! :D
I didn't know that you can store "materials" informations directedly in vertexes.
So it's not a bug just me...
I though I didn't use Clayxel the right way and the UV map of my mesh was broken or something like this
Thank you for your time.
Dranak
ps: I saw your tweet;) If you want, I will update you of my "beautiful creations."