Regression: Can't create new document after editing document type

After editing a document template/type, new documents of that type can't be saved anymore. An error dialog pops up, saying only "invalid content".

To reproduce (in Go Green or archetype):

• Log in as admin
• Go to the documents perspective
• Click "Configuration" below the folder navigation tree
• Find the "News" document type
• Click "Edit"
• Change something, then click "Done"
• Click "Type actions" and then "Commit"
• Go back to the "Documents", and open the News folder
• Create a new news document
• Enter a title, and click "Save"
  Expected: I saved a new news document
  Actual: I couldn't save. An error message appeared: "invalid content"

Line of error from the logs:
javax.jcr.ValueFormatException: not a double: preview

In the prototype, the hippo:availability property has type Double (for instance in /hippo:namespaces/hippogogreen/newsitem/hipposysedit:prototypes/hipposysedit:prototype)

Attached screenshot and stacktrace