You mentioned you're using Ruby on Rails as a backend. You didn't post the code for the relevant method, but my guess is that it looks something like this:
def create
post = Post.create params[:post]
respond_to do |format|
format.json { render :json => post }
end
end
Change it to:
def create
post = Post.create params[:post])
render :json => post
end
And it will solve your problem. It worked for me :)