[V17.1-RC] Infinite Editing: Unable to save a variant document after changing property variation setting

[nhudinh0309]

Which Umbraco version are you using?

17.1.0-rc

Bug summary

When using Infinite Editing to change a property editor's variation setting from shared property to variant property, the document becomes unsaveable. The save operation throws an error.

Specifics

No response

Steps to reproduce

Prerequisites

• A variant document type with one text string property editor configured as "Invariant" (shared across all languages)
• At least 2 languages configured in the backoffice
• Content 'A' with shared textstring value using this document type

Steps to Reproduce

1. Go to content 'A'
2. Click to open document type in the Info tab
3. Update the variant setting of the textstring property editor from shared to variant
4. Save the Document Type
5. Update value for textstring property in both languages
6. Click 'Save and publish..' or 'Save..'

Expected result / actual result

Expected Behavior
After changing the property editor variant setting, the existed value of property editor in default language should be kept and user can add value for other languages (same as V13)
And the document should save successfully

Actual Behavior
After changing the property editor variant setting, the existed value of property editor in default language is removed
And the document fails to save

Content._.Umbraco.-.Google.Chrome.2025-12-18.14-11-56.mp4

[AndyButland]

Fixed via #21221 for 17.1.