Using list controls for page collections

Wasn't sure whether to file this issue here or under plugin-form, so let me know if I should move it.

What I'm trying to do is to set up an admin blueprint that uses a list control to specify a page collection of individual pages. My blueprint looks like this:

``` yml
title: Collection
'@extends': default

form:
fields:
tabs:
type: tabs

fields:
collection:
type: tab
title: Collection

fields:
header.content.items:
type: list
label: Collection
btnLabel: Add project
style: vertical

fields:
.@page.self:
type: pages
label: Page
```

This renders the admin controls correctly, and if I enter the items in a collection manually, the admin panel will render them correctly. However, if I make edits in the admin panel and save, things will trip up on the .@page.self key, and the generated YAML will look something like this:

``` yml
content:
items:
-
'@page':
self: /projects/example
```

How can I prevent @page from becoming an object - ie. how can I make the YAML serializer "escape" the dot in the key name in the admin blueprint?

Start with the admin blueprint's list control, the .@page.self pages field, and the save path that produces YAML. Reproduce the conversion shown in the issue and trace how the key is serialized. Done means saving preserves the literal @page.self key rather than creating a nested @page object.

Written by the indexing model from the issue text.