[ZBrush] Tri Part Curve MultiMesh not working properly

Hello. I am trying to make a wired curve multimesh brush. So I have three parts: the beggining, the end, and the middle zone, as in the picture below. 



So what I want to obtain is a curve stroke where the first and third polygrups only appears once. Just like this: 



But instead, I am getting this result: 



Why is this happening? I'll appreciate an answer. Thanks in advance!