Pasting block in nested blocks fields adds block twice

[SebastianEberlein-JUNO]

Description

In a nested blocks fields, pasting a block can result in two blocks being added, under these conditions:

1. The same block name is used in both the parent and the child blocks field.
2. The block in the nested blocks field is selected, then copied and pasted using CMD+V.

When using the pasteboard, the block is only added once.

See video:

nested-blocks-copy-paste.mp4

To reproduce

In the plainkit, add these two blueprints. The article block is used both in the main blocks field as well as the two column block.

# site/blueprints/blocks/article.yml
name: Article
wysiwyg: true
preview: fields
fields:
  text:
    type: writer

# site/blueprints/pages/default.yml
title: Default Page

fields:
  blocks:
    type: blocks
    fieldsets:
      article: blocks/article

      twocol:
        name: Two Columns
        wysiwyg: true
        preview: fields
        fields:
          blocksLeft:
            type: blocks
            width: 1/2
            fieldsets:
              article: blocks/article
          blocksRight:
            type: blocks
            width: 1/2
            fieldsets:
              article: blocks/article

Your setup

Kirby Version
4.7.0

Your system
Chrome 134 on macOS 15.3.2