OPAL-Cyc: Mixing coordinates and momenta for ID0

The first two particles from the input beam are:

0.000 0.000 0.000 0.0000 0.0000 0.0000   
0.000 -0.0074186 0.0000 0.00000 0.0000 0.00000

the OFFSETZ and OFFSETY have been used in the input file: OFFSETZ = 0.15 m and OFFSETY = 0.0001 m

Outputs

Step 0

** Track-orbit: it is already known that the y and z coordinates for ID0 are not updated with respect to OFFSETY and OFFSETZ. X-coor is correct.

          x [mm]                        beta_x*gamma                       y [mm]      beta_y*gamma                     z [mm]            beta_z*gamma     
ID0 -1.30000000e+03     -3.30872245e-24     2.71050543e-17     7.41857376e-01    -2.58493941e-26      1.69406589e-21
ID1 -1.30000000e+03     -7.41860000e-03     1.00000000e-01     7.41857376e-01     1.50000000e+02      0.00000000e+00

** H5: only ID0 coordinates are copied from ID1

              x [m]      y [m]          z [m]           px                    py                    pz
ID0 *      -1.3 *    0.0001 *      0.15 *         0 *           0.7418573 *         0 *         
ID1 *      -1.3 *    0.0001 *      0.15 * -0.007418 * 0.7418573 *         0 *

Step 100

** Track-ordit

        x [mm]                        beta_x*gamma                       y [mm]               beta_y*gamma               z [mm]               beta_z*gamma     
ID0    4.91648494e+02     5.82908115e-01          2.17698321e+03      -2.50847030e-01     2.86192018e+02     3.85769984e-01
ID1   5.14833464e+02      6.81873741e-01         2.19127413e+03        -2.92328139e-01    1.50000000e+02     2.56591691e-16

** H5

               x [m]                y [m]              z [m]           px                    py                    pz
ID0 * 0.5148334 * 2.1912741 *      0.15 * 0.5829081 * -0.250847 * 0.3857699 *         
ID1 * 0.5148334 * 2.1912741 *      0.15 * 0.6818737 * -0.292328 *         0 *

Conclusions

In case of OFFSETs, the ID0 particle stored in the track-Orbits is not shifted. Depending on the simulation, the track of this particle could be wrong. For example, assuming to place the beam in the mid-plane of a dipole, as in my case, the ID0 particle sees a wrong magnetic field. In my simulation, this particle is useless, it cannot be used as reference particle and removed from the track-Orbit file.
In the H5 file, a combination of ID0 and ID1 is stored. The coordinates of ID0 are copied from ID1 (properly tracked in the simulation), while the momenta are from the track of ID0. The result is a mixture of particle coordinates and momenta.

Solutions

Update the position of the ID0 (already discussed, but too complicated)
Write a note in the manual that explains this situation
In the H5 file, copy completely ID1 and not mix two particles.