What is the intended intuition, by the way? Locomotives are all in one tab, no matter if electric or not. In the electric tab, there are electric system trains
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(is there any better expression for engines and cars that belong together exlusively?).
EMU probably. I avoided the term in this discussion so to not confuse things with the use of the term "multiple unit" in this thread before.
Non-electric system trains are in the passenger tab together with the general pax and mail cars that can go with electric and non-electric locomotives. Is that about how it should be?
It's probably not pak-specific and one gets used to it, but it is anyway far from being intuitive.
You're right it is not pak-specific, it's just "how depots work" in simutrans. To me (as a player and pak developer/maintainer, but not code-developer) it appears to work something like this:
At first it is really simple: if it is powered it goes into "Locomotives" tab, if not it goes into the "Cars" tab, (almost) regardless of freight type. But no rule without exceptions so...
...when freight type is set to either passengers or mail, the vehicle goes to "Passenger trains" tab instead (this time regardless of being powered or non-powered).
And now comes the last special case: the "Electrics" tab, which is (as far as I can tell) just a subsection of the "Passenger train" tab, just filtering all the "engine_type=electric" from that tab and leaving the rest there.
Probably not intuitive at all, but after so many years with Simutrans, people like myself have simply got used to it, I think...
Anyhow, that's all we have to work with as pak-maintainers. So, as you can see, our influence on vehicles in this matter is fairly limited.