[Bug]: Articulated vehicle bug

Version of OpenTTD

12.2

Expected result

Articulated train-car of 1+6+1 length should reverse normally

Savegame:
Articulated_vehicle_bug.zip
GRF and sourcefile:
https://github.com/Yozora3/JPplusMetro

Actual result

When articulated train-car of 1+6+1 length is reversed, bounding box flips, causing the graphical bug

Steps to reproduce

1. Load the savegame with provided GRF file
2. Reverse the train on the exact position

Possible causes

Pruple
I can confirm that in the grf posted the bounding boxes move when reversing the train...
happens with vehicles from some other grfs too, with certain train vehicle combinations.
Yozora
I have another articulated train with 1+7+1 combination that works perfect
Pruple
does it depend on the length of the train?
Yozora
I think it's connected to odd\even numbers of the middle articulated section
With developer tools I can see that 1+7+1 bounding box is in the middle, while 1+6+1 the position changes with direction of the train
Pruple
there's definitely some rounding error with certain combinations of vehicle lengths and how it calculates where to position the other end of the consist when reversing. 6-6-8 jumps, 6-8-6 doesn't.

Start by loading the provided Articulated_vehicle_bug.zip savegame with the JPplusMetro GRF, then reproduce the reversal at the exact position described. Compare the bounding-box position for the 1+6+1 and 1+7+1 articulated trains, including the 6-6-8 and 6-8-6 combinations mentioned in the discussion. Done means reversing these combinations no longer causes the bounding box to move or the graphical bug to appear.