Anyone know how AO3 coding works

[sarren]

I just attempted to copy and paste a polished version of a fic for a challenge, only to find that for some reason it's picked up one of my italicise tags early in the fic and repeat it all the rest of the way through the fic between every paragraph break. so that I've ended up with <p><i> words</i></p>

I tried the c&p from both Word and googledocs, same result.

It's quite a decent length and picking them all out individually is going to be very frustrating.

Edit: It was user error, because of course it was, AO3 is awesome.