Dynamic content rendering broken in webforms

Description

Steps to reproduce
1. Create a webform-based site using Visual studio extension (version 10.9.0 or 10.9.1).
2. Enable DynamicContent on a XhtmlString property (admin mode > Content Type tab > select content type then an xhtml string property. Select Custom Settings tab > use custom settings. Drag in Dynamic content plugin, marked with '{}'.)
3. Go to edit mode and edit an Xhtml string property.
4. Click dynamic content ('{}' button), select type "Page Property", select a page, and select property 'Name'.
5. Save and publish.
6. View the page in default and onpage edit mode.

Expected: The dynamic content item is rendered so it shows the name selected in step 4.
Actual: The dynamic content is rendered as

.