In whichSide with eps
PlaneSide whichSide ( const Plane<DATA_TYPE>& plane, const Point<DATA_TYPE, 3>& pt, const DATA_TYPE& eps )
instead of
if ( dist < eps ) return NEG_SIDE;
should be
if ( dist < -eps ) return NEG_SIDE;
because in this case we have right situation: NEG_SIDE for (-infinity, -eps), ON_PLANE for (-eps, +eps) and POS_SIDE for (+eps, +infinity)