Path reservation is not working when crossing a path signal from back side

Question

I'm trying to build a two-way railroad with 3 tracks. 2 tracks for both directions and a shared track in between which can be used in both directions for passing slower traffic on "main tracks".

I wanted to use one-way path signals on side tracks to ensure a single direction on them. On the middle track, I use regular path signals to allow any direction on it.

On the screenshot, I stopped Train11 and others got stuck behind it (I expected them to use a middle track to pass the obstacle). As I understand from the path signal descriptions, it should allow traffic from its back side. But in my example, the sign that is pointed by the red arrow prevents other trains to reserve a section on the middle track. Sometimes they pass the stopped train successfully, but most of the time they get stuck. If I remove the marked sign, trains #3, #10 and #4 will pass the stopped train successfully.

What am I missing about the path signs? Or is it some sort of a bug? Because from my understanding, this design should work just fine.

P.S. The reason I decided to place signs on the middle lane like that is to allow a train from the main track to reserve a section on a middle track only if it is not already reserved by another train going in another direction.

Answer 1

To help anybody looking for the same info, I post my solution here.

Here I modified my example. With red arrows I marked additional path signals that are required for this junction to work as expected. First they seem rudimentary. But I guess that a path going through the back of a path signal has a huge penalty and thus without these signals, a path finding algorithm will not even consider a middle lane. But once I add the mentioned signals, the penalties are pretty much equal and it can choose the middle track when it's free.

I am still surprised though that path finding algorithm prefers a blocked track to the one with a backward facing path signal. We can check it if we add 1 more path signal to the middle lane, it will break the junction again(because it will has 2x penalty now).