Huh… 
Based on this, it was taught like that on WaniKani before:
I’ve seen a lot of people, me included, write it like that as well.
Even here, it does say irregular, but it’s still there.
I did search and you’re right…
My life is a lie.
Edit: after saying it 100 times, I guess it was only a writing issue, because I don’t pronounce the extra n, it does feel weird.