I have two more one_train_staff related bugs:
Sometimes the reservation does not reserve the whole track to the next one_train_staff cabinet. First I thought this only happens when using the explained exploit, but it does also occur when used at dead-end tracks.
When this happens and another train comes to a halt at the one_train_staff cabinet, the train at the cabinet will wait in drive_by_sight (or maybe any other mode it was in, but I didn't test this) but also reserve these tiles.
When the train in the one_train_staff block returns to that tile, it will come to a halt and will wait for the track to be cleared, which will never happen.
See the attached images for this.
I don't know how to exactly reproduce this but it will happen in the savegame at layouts 6 and 8, whereas layout 7, which is exactly the same as layout 8, except being rotated by 1080° does not seem to be affected.
Also, layout 10 seems to be perfectly working, which is exactly the same as layout 6, except that the cabinets are connected diagonally.
Just unlock the deadlocked trains by stopping the one waiting at the one_train_staff cabinet and clearing the reservation of that train and watch them moving. There will be a missing reservation soon that will be reserved by the train waiting at the cabinet in drive_by_sight soon.
Yet another one:
When a train has to wait at a one_train_cabinet, its reservation will be only one tile instead of the whole train length. You can see this in on the images and in layouts 5,6,7,8,9 and 10.
Other trains can then stack at the exactly same tile and this will very likely cause a wrong reservation when the staff is returned. You can see this when you start the train in the depot of layout 7.
Furthermore, at layout 9 some poor one_train_staff cabinets are being abused for some kind of perfectly working absolute block signaling, theoretically being available even before time interval signaling was invented.