Form Input renders as raw text in cell

[HermannHH]

When rendering a form via cells & slim, the form tag is parsed properly as a <form> tag. All the inputs inside the form, however, are printed out as a string/text in the browser view.
If the same form is rendered as a Rails view, the form is parsed perfectly.

What I would expect to happen:

Render form with an input called body. Image of form using standard Rails view:

What happens

Renders the input HTML as raw text instead of an input. Image using cell.

My Code:

Gemfile

gem "trailblazer-cells" # V 0.0.3
gem "cells-rails"  # V 0.1.3
gem "slim-rails". # V 3.2.0
gem "cells-slim" # V 0.1.1

messages_controller.rb

def new
    run Message::Operation::Create::Present
    render html: concept(Message::Cell::Form, @form,
      context: {}
    )
end

application_cell.rb

class ApplicationCell < Trailblazer::Cell
  include ::ActionView::Context
  include ActionView::Helpers::UrlHelper
  include ActionView::Helpers::CaptureHelper

  include ::SimpleForm::ActionViewExtensions::FormHelper
end

message/cell/form.rb

class Message::Cell::Form < ApplicationCell

  def show
    render
  end

end

messages/view/form.slim (PS: I have also tried with a single =)

== simple_form_for model, url: messages_path, method: :post do |f|
  = f.input :body
  = f.submit

[samstickland]

I think you want - simple_form_for not ==