scriblib/footnote broken

[rfindler]

This program:

#lang scribble/base
@(require scriblib/footnote)
@(define-footnote footnote footnote-part)
abc@footnote{abc}

raises this error:

$ scribble --pdf tmp.scrbl
hash-ref: no value found for key
  key: (generated-tag)
  context...:
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/core.rkt:605:0: tag-key
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/core.rkt:24:0: resolve-get/where
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/core.rkt:62:0: resolve-get
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:758:4: resolve-content method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:758:4: resolve-content method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:758:4: resolve-content method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:758:4: resolve-content method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:758:4: resolve-content method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:758:4: resolve-content method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:725:4: resolve-flow method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:713:4: resolve-part method in render%
   loop
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/base-render.rkt:705:4: resolve method in render%
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/render.rkt:33:0: render57
   /Users/robby/git/plt/racket/collects/racket/contract/private/arrow-val-first.rkt:397:3
   /Users/robby/git/plt/extra-pkgs/scribble/scribble-lib/scribble/run.rkt: [running body]

This program worked in 5.3.3, but not in 5.3.4.