Bug in UniaxialStrainer ?

Hi people !

I encountered problem that was solved by modifying this part [1].

Problem :

box shaped specimen, UniaxialStrainer axis is vertical (axis =2), forces are applied on lateral surfaces (axis 0 and axis 1)
upper spheres (posIds) and lower spheres (negIds) should move along axis 2 only, but they move along axis 0 and axis 1 also, making the crossSection smaller than it should be which creates an additional shear force that will inevitably break the links between those spheres and the specimen.

Fix :

replace :
b->state->vel[axis]=pNormalized*(v1-v0)+v0;

by :
switch(axis){
   case 0: {
    b->state->vel[0]=pNormalized*(v1-v0)+v0;
    b->state->vel[1]=0;
    b->state->vel[2]=0;
    break;
    }
   case 1: {
    b->state->vel[0]=0;
    b->state->vel[1]=pNormalized*(v1-v0)+v0;
    b->state->vel[2]=0;
    break;
    }
   case 2: {
    b->state->vel[0]=0;
    b->state->vel[1]=0;
    b->state->vel[2]=pNormalized*(v1-v0)+v0;
    break;
    }
   default: throw std::invalid_argument(("UniaxialStrainer: unknown axis value "+boost::lexical_cast<string>(axis)+" (should be 0,1,2)").c_str());

Am I the only one facing this problem ?

Cheers,
Hicham

[1] : https://github.com/yade/trunk/blob/master/pkg/dem/UniaxialStrainer.cpp#L77