scarakins axis follow problem in -x and -y zone

        *iflags = 0;
           if (joint[1] < 90)          
           *iflags = 1;



than in Inverse:

[code]    /* joint 1 angle needed to make arm length match sqrt(rsq) */
    cc = (rsq - D2*D2 - D4*D4) / (2*D2*D4);
    if(cc < -1) cc = -1;
    if(cc > 1) cc = 1;
    q1 = acos(cc);
    if (*iflags)
    q1 = -q1;



but not understand why exactly seems x and c axis try to moove into undesired point (with estop obtain follow error on joint 0 and joint3 so X and C axis) ... these not happens in positive area +X and +Y or +X and -Y or -X and -Y ... only during moovement trought -Y to +Y if I'm on -X area ..... but is these logical?  a3 or C axis not change angle during these motion from -n to +n or inverse ....

any suggestion is appreciate

p.s.:
axis limit for test is set to +6000mm and -6000
mm... but robot can reach only 900mm. joint limit is set to +720° and -720° so is not a limit problem ...

static int scaraKinematicsInverse(const EmcPose * world,
                                  double * joint,
                                  const KINEMATICS_INVERSE_FLAGS * iflags,
                                  KINEMATICS_FORWARD_FLAGS * fflags)
{
    double a3;
    double q0, q1;
    double xt, yt, xt1, yt1, rsq, cc;
    double x, y, z, c;

    x = world->tran.x;
    y = world->tran.y;
    z = world->tran.z;
    c = world->c;

    /* convert degrees to radians */
    a3 = c * ( PM_PI / 180 );

    /* center of end effector (correct for D6) */
    xt = x - D6*cos(a3);
    yt = y - D6*sin(a3);
    xt1 = xt;
    yt1 = yt;

    /* horizontal distance (squared) from end effector centerline
        to main column centerline */
    rsq = xt*xt + yt*yt;
    /* joint 1 angle needed to make arm length match sqrt(rsq) */
    cc = (rsq - D2*D2 - D4*D4) / (2*D2*D4);
    if(cc < -1) cc = -1;
    if(cc > 1) cc = 1;
    q1 = acos(cc);

    if (*iflags)
        q1 = -q1;

    /* angle to end effector */
    q0 = atan2(yt, xt);

    /* end effector coords in inner arm coord system */
    xt = D2 + D4*cos(q1);
    yt = D4*sin(q1);

    /* inner arm angle */
    //q0 = q0 - atan2(yt, xt);
    if((xt1<0) && (yt1>=0)){q0 = q0 - atan2(yt, xt) - 2*M_PI;}
    else{q0 = q0 - atan2(yt, xt);}

    /* q0 and q1 are still in radians. convert them to degrees */
    q0 = q0 * (180 / PM_PI);
    q1 = q1 * (180 / PM_PI);

    joint[0] = q0;
    joint[1] = q1;
    joint[2] = D1 + D3 - D5 - z;
    joint[3] = c - ( q0 + q1);
    joint[4] = world->a;
    joint[5] = world->b;

    *fflags = 0;

    return (0);
} // scaraKinematicsInverse()