Re: kbd vs read-key-sequence

[Richard Stallman]

    Yeah, probably.  But it's been the case sine Emacs-20.  And some of the
    bindings which worked in Emacs-20 failed in Emacs-21, and some of the
    binding that work in Emacs-21 will fail in Emacs-22, and the same for
    Emacs-23 most likely.  And if you add modifiers it's even more likely
    to fail.

I was not following this thread.  Can someone summarize the problem
as it is known?  And is it only on Windows, or is it for all systems?
(I've seen both statements made.)