Strange warning message from M-x byte-compile-file

[Alan Mackenzie <acm@muc.de>]

GNU Emacs 21.3:

This has been puzzling me for ages:  I do M-x byte-compile-file, it runs
without error, yet leaves this bizarre warning in *Compile-Log*:

  ** The function `acm-texinfo-end-of-node' might not be defined at runtime.

That function is a straightforward defun in my site-start.el, followed by
(byte-compile 'acm-texinfo-end-of-node).  I bind it in Texinfo mode
thusly:

(eval-after-load "texinfo"
  '(progn
     (define-key texinfo-mode-map "\C-\M-a" 'acm-texinfo-beginning-of-node)
     (define-key texinfo-mode-map "\C-\M-e" 'acm-texinfo-end-of-node)
     (define-key texinfo-mode-map "\C-xnd" 'acm-texinfo-narrow-to-node)))

Can anybody give me a clue why I'm getting this warning message, time
after time after time?  It's beginning to get on my nerves.

Thanks in advance.

-- 
Alan Mackenzie (Munich, Germany)
Email: aacm@muuc.dee; to decode, wherever there is a repeated letter
(like "aa"), remove half of them (leaving, say, "a").