Blueprint block grid preview shows wrong content

Symptom

When editing a Document Blueprint in Settings > Document Blueprints, block grid blocks that read from the parent document’s properties via Umbraco.AssignedContentItem display content from an existing published page instead of the blueprint’s own property values.

For example, a “Feature - Page - Title and Description” block that renders @currentPage.PageTitle shows “The Moorish Treasures of Andalucia” (from an existing Tailored Tour page) instead of [Page Title] (the blueprint’s placeholder value).

Blocks with their own stored values (e.g. Rich Text Editor blocks with inline content) are not affected - they display and save correctly in the blueprint editor.

Cause

This is an Umbraco core issue with how Umbraco.AssignedContentItem is resolved during block grid server-side rendering (SSR) previews.

When a block’s Razor partial reads from Umbraco.AssignedContentItem, the resolution chain in UmbracoViewPage.cs is:

1. Check if the view model is IPublishedContent - it’s a BlockGridItem, so no
2. Check if the view model is IContentModel - it’s not
3. Fallback: use UmbracoContext.PublishedRequest.PublishedContent

The fallback is the problem. Blueprints are not in the published content cache (IsBlueprint = true, draft-only items). So PublishedRequest.PublishedContent resolves to whatever published content was last in context - typically an existing page of the same document type.

Key source files in Umbraco CMS:

• src/Umbraco.Web.Common/Views/UmbracoViewPage.cs - where AssignedContentItem is set
• src/Umbraco.Web.Common/Templates/TemplateRenderer.cs - where PublishedRequest.PublishedContent is determined

Impact on UpDoc

This is a cosmetic issue in the blueprint editor only. It does not affect UpDoc’s content creation pipeline:

• The blueprint’s stored data is correct (confirmed via uSync XML export)
• When UpDoc creates a real document from the blueprint, AssignedContentItem resolves to the new document with the correct page properties
• The editor will see the correct values on the created page

Workaround

There is no workaround within the blueprint editor. The preview will show stale content from an existing page regardless of what the blueprint’s page properties contain.

Options:

1. Accept the cosmetic issue - the blueprint data is correct even though the preview is misleading
2. Use a real content page as a reference - create and maintain a [Tailored Tours Blueprint] content node alongside the actual blueprint, so you can verify the block grid layout on a real page
3. Edit via uSync XML - modify the blueprint’s uSync/v17/Blueprints/*.config file directly and import via uSync. The blueprint GUID is preserved, so workflow configurations remain valid.

Umbraco issue

Reported to Umbraco CMS: umbraco/Umbraco-CMS#21919

Affected versions

• Umbraco CMS v17 (confirmed)
• Likely affects all versions using block grid SSR preview in blueprint editor