Seemingly simple... Panel blueprint "File Max:1" not working

This seems like a rather straightforward thing but, despite having a Max:1 in the blueprint, the panel still allows more than 1 file to be uploaded. I’m not seeing any errors and can’t find anyone else experiencing the same issue, so I’m assuming it is something really silly on my part. Here’s my full blueprint:

title: FAQ
pages: false
files:
  max:1
  fields:
    caption:
      label: Caption
      type: textarea
options:
  preview: false
  status: true
  template: false
  delete: true
  url: false
fields:
  title:
    label: Question
    type: title
  text:
    label: Text
    type: simplemde

There’s a space missing between the colon and the number, should be:

max: 1

If you use a text editor with support for yaml, you will immediately see that the syntax is wrong :

28 13

Wow, “something really silly on my part” indeed. Thanks very much for your patience.