In login.jelly, this uses SimplePageDecorator instead of the typical PageDecorator used on most other pages. The latter decorator supports registering multiple instances so that they can all be included in various pages. The former, however, only uses the first instance found. By doing this, plugins cannot override the default login page decorations without needlessly copying code from Jenkins Core to emulate it.
What I'd like is for the login page to list out all registered decorators for the footer in order rather than just the first one.
This also applies to the signup.jelly page.