What in the world is happening with castoroides and protosciurus?

For the last month or so, these two buildfarm animals (which I believe are
the same physical machine) have been erratically failing with errors that
reflect low-order differences in floating-point calculations.

A recent example is at

http://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=protosciurus&dt=2014-08-25%2010%3A39%3A52

where the only regression diff is

*** /export/home/dpage/pgbuildfarm/protosciurus/HEAD/pgsql.22860/src/test/regress/expected/hash_index.out Mon Aug 25 11:41:00 2014
--- /export/home/dpage/pgbuildfarm/protosciurus/HEAD/pgsql.22860/src/test/regress/results/hash_index.out Mon Aug 25 11:57:26 2014
***************
*** 171,179 ****
SELECT h.seqno AS i8096, h.random AS f1234_1234
FROM hash_f8_heap h
WHERE h.random = '-1234.1234'::float8;
! i8096 | f1234_1234
! -------+------------
! 8906 | -1234.1234
(1 row)

UPDATE hash_f8_heap
--- 171,179 ----
SELECT h.seqno AS i8096, h.random AS f1234_1234
FROM hash_f8_heap h
WHERE h.random = '-1234.1234'::float8;
! i8096 | f1234_1234
! -------+-------------------
! 8906 | -1234.12356777216
(1 row)

UPDATE hash_f8_heap

... a result that certainly makes no sense. The results are not
repeatable, failing in equally odd ways in different tests on different
runs. This is happening in all the back branches too, not just HEAD.

Has there been a system software update on this machine a month or so ago?
If not, it's hard to think anything except that the floating point
hardware on this box has developed problems.

regards, tom lane