[5.x]: Revision views allow copying nested entry blocks, but pasting does not work

[superflausch]

What happened?

Description

The revision view for entries exposes actions to copy blocks (nested entries), but the behavior does not match user expectations and feels more like an unintended UI oversight.

From what I can tell, the behavior differs depending on whether the block/entry still exists in the current live version of the parent entry:

• If the block/entry no longer exists in the current/live version of the parent entry, the Copy action does nothing.
• If the block/entry still exists and has no nested entries of its own, the user can copy it and is shown valid paste targets, but nothing happens after pasting.
• If the block/entry still exists and contains nested entries itself, the user can copy it and is shown valid paste targets, but pasting triggers this error: “An error occurred when duplicating the element.”

We received reports from users who tried this and were unable to make it work. I was also able to reproduce the behavior on a clean setup. See the attached video for a demonstration.

Steps to reproduce

1. Create a content model like this:
   Pages (Section) → Page (Entry Type) → Sections (Matrix field, "Cards" view mode) → Section (Entry Type) → Blocks (Matrix field, "Blocks" view mode) → Rich (Entry Type) → Rich (CKEditor field)
   Add additional entry types within Blocks, including some that contain nested entries themselves, so that different cases can be tested.
2. Create content in Sections with several Blocks.
3. Create revisions by making changes and deletions.
4. Open a revision view.
5. Try to copy blocks from the revision and paste them into the current/editable version.

Expected behavior

Users should be able to copy all supported block types from a revision and paste them into any applicable position, in the same way this works from the current/editable version of an entry.

Actual behavior

Pasting fails. In some cases, nothing happens at all; in other cases, an error is thrown.

Screen.Recording.2026-03-30.at.14.58.03.mov

Craft CMS version

5.9.18

PHP version

No response

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions

• CKEditor 5.3.1

[linear]

CMS-1933

[i-just]

Hi, thanks for reporting! I raised a PR for this.