This is an old topic but someone mentioned it irritates you when people write OOC ...what is the point of writing a "fanfiction" if you are going to write another episode of the same fandom. I mean seriously; if you need other chapters/episode of whatever fandom you are in...then you are not writing; fanfiction...you are copy writing. Sorry for the pun there but that is my opinion.
I have written an extremely successful series that I follow canon of the stories in the details but that is "the past". My series sets the same characters with their own futures and issue. Issue being family, etc. It has been very well received. While I try to maintain the characters from my fandoms as close as I possibly can; again...I am writing an emulation of a favorite story and continuing it as it were.
While you're right, authors have the liberty to write the characters any way they wish, most people don't really like it when, say, Harry Potter is written as a happy-go-lucky twit with severe shyness. At some point it just becomes a turnoff. :) I'm sure there are lots of people who enjoy having characters written differently, but most people don't.
I have written an extremely successful series that I follow canon of the stories in the details but that is "the past". My series sets the same characters with their own futures and issue. Issue being family, etc. It has been very well received. While I try to maintain the characters from my fandoms as close as I possibly can; again...I am writing an emulation of a favorite story and continuing it as it were.