SA-MP bug, impossible to fix.
Locked.
I'm sorry, when did you suddenly join the development team? :/
Something happens, I don't know what, to cause NPCs to be ejected from their vehicles. I'm wondering if cheaters are able to do this by warping into the train.
If I can get a test working for this to repeatedly cause it using cheats, I can script a fix and put the train drivers back, and ban the offender. For now I think I will reset all NPCs on a city change so it fixes itself.