Face flip or disappears when in-game.

Celths

Hello, i've a problem, when i test in-game my leshrac's tail, somes faces disappears directly or flip when i switch ''portrait preview'' to ''body preview''.
I've try to change the skinning, faces, uvs, remake the object... but nothing change.

Faces that disappear are in the middle and at the end of the tail.

thanks for yours answers.

Celths

I've test the basic model, exported in .FBX and .SMD with 3dsmax 2010, with 1 color texture for mask1 and 2 and base texture, same problem.