[Self-hosted] Registration form still requires Email and treats Username as optional when Sign-in Method is set to Username-only

When adding a new account via Manage accounts on a self-hosted instance whose Sign-in Method is restricted to Username only, the “Create an account” form still behaves as if email-based sign-in were enabled: The Email field is shown (and appears to be required). The Username field is labeled (optional) with the placeholder “Leave blank for a random username”.

Set up a self-hosted Fluxer instance. Configure the instance so that the only enabled Sign-in Method is Username. In the client, open Manage accounts → add/register a new account. Observe the “Create an account” form.