pg_upgrade: when the --old-bindir requires "additional" $libdir/ plugins?

Hi all,

with a huge delay, I've seen this question [1].

. and it seems like the hstore.so was somewhat intimately integrated into
OP's database so the '/usr/bin/pg_dump --schema-only --binary-upgrade
--format=custom' called through 'pg_upgrade' failed with:

pg_dump: [archiver (db)] query failed: ERROR: could not access file
"$libdir/hstore": No such file or directory

Which means that the dump from old datadir, with old server (without
hstore.so packaged) failed. But playing with hstore.so a bit, the upgrade
always worked smoothly for me even without the "old" hstore.so

Googling around, I only found that there were some incompatible changes
historically in hstore.so causing pg_upgrade failure; but this is
different issue -- in the issue I talk about now the module was not found
at all, even though it is usually even not searched for.

So the question is what circumstances could cause this issue in
particular? Is it expected in general that, to make the pg_upgrade run
smooth, all the "loaded" server modules are built against and available
for the --old-bindir server? Don't we have some reproducer for this
kind of issues?

[1] https://ask.fedoraproject.org/en/question/69316/postgresql-doesnt-work-after-upgrade-to-f22/
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1557490

Thank for hints,
Pavel