I recently hit a bug in a recent build of GNU Emacs. The crux of the matter was that word-relative functions such as forward-word now respect subword-mode and superword-mode. This is good for interactive use, but can have unintended consequences in existing code, which is what happened with ERC: ERC expected forward-word to move consistently, but now it behaves differently if subword-mode is active.

The solution seems to be to forgo forward-mode and friends for interactive use, and to use more low-level functions in programs. For instance, I replaced (upcase-word 1) with

(skip-syntax-forward "^w")
    ((word-start (point))
      (progn (skip-syntax-forward "w") (point))))
  (upcase-region word-start word-end))

Way more verbose than I would like, but it works.