dblink crash on PPC

Something odd is happening on buildfarm member wombat, a PPC970MP box
running Gentoo. We're getting dblink test failures. On the one I looked
at more closely I saw this:

[4ddf2c59.7aec:153] LOG: disconnection: session time: 0:00:00.444 user=markwkm database=contrib_regression host=[local]

and then:

[4ddf2c4e.79d4:2] LOG: server process (PID 31468) was terminated by signal 11: Segmentation fault
[4ddf2c4e.79d4:3] LOG: terminating any other active server processes

which makes it look like something is failing badly in the backend cleanup code. (7aec = hex(31468))

We don't seem to have a backtrace, which is sad.

This seems to be happening on the 9.0 branch too.

I wonder what it could be?

cheers

andrew