Unicode assignation scrambled after OT-TTF generation

I am having a very weird behaviour with a client's font family: if I generate in Fontlab the font as PS1 flavored OT there is no problem, but after converting to TTF contours, when I use the same workflow to generate a TTF flavored OT, the resulting file have almost all unicodes scrambled and wrongly assigned. Any idea? It is the first time something like that happen to me.