gcampono, you can download my save.
it`s a big map. 1850year. and horse line through the entire map.
line has 4 stops, but 1,2 and 3,4 is the same stopgroup.
i.e. line:
1. A
2. A
3. B
4. B
This is necessary because on the line (1.A, 2.B), this bug is not reproduced.
The same can be done with trains. To do this you can add a reversal loop after each station.