The fact that you haven't even posted your trainers.txt doesn't help. I can only say that I've edited these files directly myself, and I don't have a problem, so you must be doing something wrong.
Sorry, I missed the "unmodified". Well I found by luck what it was yesterday so I'm posting it here just for the sake of reporting it. It looks like the .txt was corrupted and couldn't be read by the engine whenever I edited it directly. Copying all the content into a fresh .txt worked as a miracle so it wasn't my fault either.