8.4.0 vs. locales vs. pl/perl?

Having been helping someone out on IRC with what looked initially like
an index corruption problem, it turns out to be (almost certainly) a
locale initialization error.

environment: debian packaged 8.4.0

scenario: restoring a dump results in incorrect indexes for some
specific tables (indexscan order fails to match < comparison or
order resulting from explicit sorts). The dump contains plperl
and plperlu language creation and function definitions; excising
these from the dump removes the problem.

The db locale is en_US.UTF-8 (which appears to be case-insensitive on
this platform: 'C' > 'd' > 'X'), but the incorrect index ordering that
results when the full restore is done is consistent with C locale
(i.e. 'C' > 'X' > 'd').

Looking at the code, the obvious thing that glares out is that the
locale setup in CheckMyDatabase is calling setlocale rather than
pg_perm_setlocale... am I missing something, or is this an obvious
bug?

--
Andrew (irc:RhodiumToad)