Why does YAPF abort here?

[[OpenTTD]Johannes]

Hi,

I made a fork of OpenTTD to implement a new feature. The new feature calls YAPF, but I get a NOT_REACHED (the only one currently in yapf_base.hpp). Since I wondered why, I ran gdb ran gdb. I also made a picture of the output.

fanfield.png (710.58 KiB) Viewed 1478 times

As one can see, the algorithm does this:

1. 82 (South-West) -> 85 (SW)
2. 85 (SW) -> 86 (SW)
3. 86 (SW) -> 87 (NE)
4. 87 (NE) -> 81 (NE)
5. 82 (NE) -> 81 (NE)

In step 4, it puts 81 into the closed list. In step 5, it discovers a closed node (81) with a shorter estimate than before, which leads to a bug.

What I don't understand is:

1. Why does it jump from 87 to 81?
2. Why does it then stop (in step 4) when it arrives at 81, instead of expanding it?
3. Finally, why does it add 81 as a closed node?

If you'd like to try it out yourself, clone git@github.com:JohannesLorenz/OpenTTD.git and use the map "testanlage5.sav" from git@github.com:JohannesLorenz/openttd-maps.git .

Many thanks for any help.
Johannes