Ship changes line on its own

[zook2]

A weird one (and reproducible):
on the BB server, go to the dock at 217,600 (password: pw). Buy a boat, set the line to "#- Welsh Potatoes". It shows up in the line list in the white font. Launch it. A second later it disappears from the potato line and is now in "#- Welsh Bulk & Goods".

[zook2]

Confirmed now. If I have two lines with identical stops (e.g. one freight line and one cargo), the game often auto-assigns a new convoy to the other line (perhaps based on some kind of internal line ID?) and not the one I selected in the depot. A second after leaving the depot my "Foo - Bar Express" passenger train slips into "Foo - Bar Cargo Express". After manually reassigning it, everything's OK.

[Mariculous]

I'm not sure if this is a bug or a feature...
What's going on is that that the line comparator method used to compare schedules is used to select a line with the same schedule.
If they match, the first matching line will be assigned.

[Matthew]

It seems that this can be worked around relatively easily using waypoints. But it's undocumented and confusing, especially for new players.

[Mariculous]

Definitely. This is confusing and should be fixed.

I am not exactly sure about the intention of this code.
This behavior seems to be meant to re-assign the original line of a convoy when it's leaving the depot as the line is unassigned when a convoy enters the depot.
This method (schedule_t::matches) is based on more than just the waypoints. It does also account for the schedule options.

I am wondering if instead of this admittedly confusing re-assignment mechanism, convoys should instead "simply"* not un-assign their line when entering a depot.
The same can be observed in further cases, e.g. when changing the schedule of a convoy outside of the depot.

*I did not yet check how simple this actually is.

[Ranran(retired)]

I am trawling through past bug reports. Because we may find something new or have a chance to solve the bug. (´・ω・｀)
I recently noticed that there is such a specification in the standard. It seems that it is not possible to make each convoy belong to multiple lines with duplicate schedules. It is aggregated on one side.
I don't know if it was brought to extended by the merge, or if it is an original specification.

[jamespetts]

I believe that this is a long established original feature dating from before Extended was forked from Standard.