[BUG] Weird behavior when passing signals from the back

[Mariculous]

When passing signals from the back, these will be handled partially.
This appears to happen only in rather rare cases of track/signalling layout, but in these it happens consistently.
I was not able to reproduce this in a minimal save, so I uploaded the server save of pak192.comic.

Reproduction:
1. Load this savegame. The pakset can be found here
2. The relevant windows should already be opened, otherwise make sure you are observing (528) Elektrolokomotive Re 420, including its working methos in the details as well as koords (1646,1146) and (1620,1136)
3. Wait a moment, the train will depart very soon.
4. On departure, the block wil lcorrectly be expanded to the next signal.
5. Shortly after departure, the train will pass an ETCS choose board from the back a few moments later, it wil switch to cab signalling.
6. Shortly after pasing the stop signal at (1711,1205) from the back, the train will expand its reservation.
    Note: If the track around (1620,1136) was not cleared at that time, the reservation would only expand to the signal at (1624,1139).