Form is never processed

I've been trying to create an as-simple-as-it-gets form (i.e. copying the example from documentation minus captcha), but the form is never processed.

I also tried removing the whole 'email' block (email settings are working) so the form should only be saved, and even with only the "message:" and "display:" statements in the process-block absolutely nothing happens except the form being reset.
I can basically add or omit whatever I want in the "process:" block, as it doesn't have *any* effect.

markdown for the page:

```
title: Contact
form:
name: contact
fields:
-
name: name
label: Name
placeholder: 'Enter your name'
autofocus: true
autocomplete: true
type: text
validate:
required: true
-
name: email
label: Email
placeholder: 'Enter your email address'
type: text
validate:
rule: email
required: true
-
name: message
label: Message
size: long
placeholder: 'Enter your message'
type: textarea
validate:
required: true
buttons:
-
type: submit
value: Submit
process:
-
save:
fileprefix: feedback-
dateformat: Ymd-His-u
extension: txt
body: '{% include ''forms/data.txt.twig'' %}'
-
message: 'Thank you for your feedback!'
-
display: thankyou
```

I also tried enabling debug and inline errors in the plugin settings, but no debug information or errors are shown or logged...