spoonbill - rare buildfarm failures in test_shm_mq_pipelined()

Spoonbill is very rarely (ie once every few months) failing like this:

[2016-08-29 18:15:35.273 CEST:57c45f88.52d4:8] LOG: statement: SELECT
test_shm_mq_pipelined(16384, (select
string_agg(chr(32+(random()*95)::int), '') from
generate_series(1,270000)), 200, 3);
[2016-08-29 18:15:35.282 CEST:57c45f88.52d4:9] ERROR: floating-point
exception
[2016-08-29 18:15:35.282 CEST:57c45f88.52d4:10] DETAIL: An invalid
floating-point operation was signaled. This probably means an
out-of-range result or an invalid operation, such as division by zero.
[2016-08-29 18:15:35.282 CEST:57c45f88.52d4:11] STATEMENT: SELECT
test_shm_mq_pipelined(16384, (select
string_agg(chr(32+(random()*95)::int), '') from
generate_series(1,270000)), 200, 3);

Some examples:

http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=spoonbill&dt=2016-10-22%2023%3A00%3A06
http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=spoonbill&dt=2016-08-29%2011%3A00%3A06
http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=spoonbill&dt=2016-06-21%2023%3A00%3A06

Any ideas on what is causing this? IIrc we had issues with that specific
test on spoonbill (and other sparc based boxes) before so maybe we
failed to fix the issue completely...

Stefan