Modular page items order through blueprint array

I tried to make a blueprint for a modular page in blueprints/modular.yaml to order modular page items.

As described in the skeletons, I tried to override the content.order.custom key and it's array items in the page with the modular template and the following custom order:
--- yaml
custom:

• _slider
• _categories
  YAMLCopy

  through a drag and drop array list in the `modular.yaml` blueprint (truncated):
  --- yaml
  header.content.order.custom:
  type: array
  value_only: true
  

  It works. The blueprint can manipulate the entries in content.order.custom, but, when I drag and drop, the blueprint form changes the list type into an indexed hash:
  --- yaml
  custom:
  1: _categories
  0: _slider

  TXTCopy

  
  therefore, the order does not really change, as the page.collection method (correctly) interprets the indexed hash as an array by using their (unchanged) index.
  

Any suggestions how to solve that issue?

Ordering modular page items could be so simple with that blueprint.