[[Special:UserLogin]] is missing a link to signup form when user is logged in. This appears to be the intended behavior (per LoginForm#showCreateOrLoginLink), but is rather annoying when a logged-in user wants to create another account.
This is rarely useful on Wikimedia wikis, which have a very open model (although even there sometimes it's useful to e.g. create account for user using banner IP range), but some third-party wikis use a more closed model where only site admins can create accounts – for them it's an important regression, as the previous form always had the link.
(As reported on MediaWiki-General a few minutes ago.)