Setting readonly on a single user select field on Service Desk makes the field look hidden in the portal view

To reproduce:

• Ensure you have a service desk project created.
• Add a single user picker field to one of the screens for the project, and then add it to one of the request types.
• Set up a Behaviour to make the field read-only.
• Go to the service desk project's customer portal and create/edit a ticket of the appropriate request type.

Expected behaviour: The user picker field is present on the screen with its value (if any) visible, but cannot be edited.

Actual behaviour: The field is present insofar as its label is visible, but the input element itself (and hence any value it might contain) is not visible.

Looks like: