I would call this bug inconsistent at best? It doesn't happen all the time, and when a train starts behaving it usually works for a while. Other times, it just will not load at all without constant micromanagement. Safe to say, causes plenty of backup on the rails, and a good couple of laughs in our group when we realize that our entire rail network got taken down by a steam train which decided to take a nap.

Hey, how have you managed to get your locomotive watered up as mine just seems to refuse to accept normal water (only thing I can think of atm is maybe a mod conflict)

Are either of you using the AAI Industries mod? I noticed the same problem: When I initially place the locomotive it fills with water, but after that it won't refill. The only way to get it to fill up again that I've found is to remove the locomotive and place it again. Disabling AAI Industries fixes the issue for me.