Re: C-m mapping fails occasionally

[Richard Stallman]

    Yeah, the whole point was that my re-mapping would only work for a while,
    then would quit working.

It looks like the global binding that you set up still exists.
How about evaluating

(key-binding "\C-m")

which will show which binding Emacs actually sees for C-m?

Also try

(mapcar (lambda (map) (cons map (lookup-key map "\C-m")))
        (current-active-maps))