Writing backwards !

Well at least in the wrong order !

Two nights ago, about 1 am I woke up with the ending of book three buzzing around in my head, and in the horrible process of having to be up and writing it, the scene before that came to me.

So what is with this backwards story telling…. I hear its pretty common. I know in my other stories I write out of order, never holding myself to order although I prefer it, but I have never gotten the end of it this early, and been so certain of it !!
So I am wondering is this common with anyone else other than me ?