It seems that with the following format of xyz:
<number of objects>
comment line
<x> <y> <z>
<x> <y> <z>
...
<x> <y> <z>
track_xyz doesn't work (which is weird because it should)
temporary solution
use this input format instead:
<number of objects>
comment line
<name> <x> <y> <z>
<name> <x> <y> <z>
...
<name> <x> <y> <z>
I'm going to investigate more on this (ASAP) and i'll update the discussion.