All upid values are -1 when using SubhaloPhaseSpace

Low priority issue, but confusing enough that I thought I'd submit an issue so it's documented.

When using SubhaloPhaseSpace (not sure it this also happens with others), the upid value for all of the satellite galaxies is -1. My understanding is that this upid == -1 indicates that the subhalo is a host halo (the highest in the halo hierarchy), basically a shorthand for saying halo_id == halo_hostid. However, all the satellites are getting upid == -1 even though their halo_id != halo_hostid.

Shortened version: Rather than getting the halo_id for their host halo in the halo_upid column, satellite galaxies are getting upid == -1 when using SubhaloPhaseSpace.