The internet always has the answers:

@HaloWell, clearly everyone on this thread got the jist of what I meant so there is no harm done mate

<Snipped quote by Halo>

Oh, wasn't that part of that big romanized spelling change that they did? I remember hearing some random tidbit of info on it a while back.

EDIT: Apparently I'm like super-wrong about the senpai/sempai thing. At least pronounciation-wise (see Anime_Freak's post.) The romanisation is still "senpai".

ORIGINAL: Back in '54? Yeah, it was when the Japanese government were trying to figure out which romanisation system to adopt.

In '30 they put up a committee to figure it out and finally decided on Nihon-shiki (now known as Kunrei-shiki) in '37. But the US being the US, in '45, after WWII, the occupying Allies came in and declared Hepburn to be the official system, because apparently Nihon-shiki had "militaristic associations" or some bollocks. It wasn't until '54 that the Japanese government officially confirmed a slightly-modified Nihon-shiki as the official one again. Hepburn 3rd edition - also known as modern Hepburn, the one that made this change - was released the same year. Funnily enough Hepburn is actually the most used system today. I use/used it in class while learning hiragana.

Anyway, that's the only occasion I can find reference to in which there was enough simultaneous change to maybe be considered "major". Idk maybe I'm looking in the wrong places.

<Snipped quote by Halo>

@Halo I'm happy that you are taking time to express concern for the misinterpretation of the Japanese language, but as someone who has been speaking Japanese almost their entire life, I have to make some tweaks to your explenation.
We use sempai and senpai together, actually. When we are addressing someone we admire as a tutor or teacher, we use sempai. This term is used for a senior that you respect normally.
When using senpai, you would use it to address someone that you find as an upperclassmen or senior that you admire with a passion.
Some people interchange them in speech, finding that the person they are addressing fits both descriptions, and that's okay.

Edit: Excuse the mispelled words. I fixed them, but obviously my English needs help xD

Then I've been misinformed by the internet. Curses. :P "Senpai" is indeed the correct romanisation though - I actually wrote a section detailing why "m" was used instead in the traditional Hepburn (something along the lines of what you're saying although I didn't realise the change in pronounciation was deliberate) but deleted it 'cause the post was way too long or something.
And to be honest it wasn't really meant to express concern or turn into a discussion - it was a frivolous comment I thought someone interested in anime/Japanese culture (i.e. the OP) would want to know.

@HaloWell, clearly everyone on this thread got the jist of what I meant so there is no harm done mate

Yeah it wasn't really meant to be a criticism - more trying to be helpful than anything. ^_^ you'd be surprised how vicious some anime and manga fans get when you mispronounce or misspell something...

<Snipped quote by ClocktowerEchos>

Yeah it wasn't really meant to be a criticism - more trying to be helpful than anything. ^_^ you'd be surprised how vicious some anime and manga fans get when you mispronounce or misspell something...

Trust me, I know. I'm one of them XD

it is a good idea to just go ahead and show them your own senpai.

<Snipped quote by Anime_Freak>

.-.-.
And to be honest it wasn't really meant to express concern or turn into a discussion - it was a frivolous comment I thought someone interested in anime/Japanese culture (i.e. the OP) would want to know.

@Halo Oh *laughs nervously* Sorry. Guess I got a little carried away. :3 Sorry bout that

Alternatively you could always walk about Boston pressing X to scream for Shaun.

<Snipped quote by ClocktowerEchos>

Yeah it wasn't really meant to be a criticism - more trying to be helpful than anything. ^_^ you'd be surprised how vicious some anime and manga fans get when you mispronounce or misspell something...

Mainga.

Hm, a cute bouquet of baguettes (or plungers) will impress them.
Or.
You can start to run around them and shout out the gloomy quotations from "Crime and Punishment".
These actions will make you look like a creative and mysterious person. Probably.