Ok, i see the problem. I assume you are applying a fixed Y rotation, and then random rotation on Z. Please, try this:
1) Set to 0 all Fixed rotations.
2) Set Y rotation using random parameters with a fixed range. I.e. from 45º to 45º.
3) Set random Z rotation as usual.
4) Be sure Segment->Transform->Random->Transfom affects size is off.
5) Set Segment->Alignment to Pivot.