>Hm, yes, that seems plausible... if you've got one API that's counting
>UTF-8 characters -- and another one that's counting bytes -- and the
>code is using these counts to index into a flat text file, and
>expecting them to agree...that seems very much like something that
>could go sideways quite easily.
>
>It also seems like the sort of thing where a system upgrade could
>"helpfully" change APIs' behaviors in the scripting language.

Further investigation, inferring based on some Googling that the forum is written in Perl -- Perl has indeed mucked about a lot with its UTF-8 support in recent-ish versions (recent compared to the age of the forum software, anyway).

Does the forum's environment have any of PERL_UNICODE, LANG, or any LC_ variables set?

Alternatively, if this undirected speculation -- debugging without information -- is unhelpful and/or annoying, please tell me to stop!