This strange to me, I have not experienced this type except the common one "while you were ready, someone has posted" is it that, it happens only in selected accounts? But I have experienced it in BTT that after trying and clicked the post button then it would write, "this thread does not exist" and that means either the thread was locked or deleted or moved out from the original position and i think that is what happened to the thread you were committing on. And as Admin said "Moved to Bug", meaning it is no longer there again. But yours strange because as you said, it happened and you rewrite it again and it goes so that is another explanation needed.