More data:

I've been unable to replicate this behavior on Ubuntu 15.04 on Python 3.4.3 over ~20 thousand test runs. (Same machine, running in a VM)

An overnight repeated run on the original machine on OS X, 3.4.3, official distribution gave an actual frequency of 0.1% (7 crashes in 6980 runs).

Approximately 3,300 runs on Python 2.7.9 on the same machine have not resulted in any crashes.

I now built 3.4.3 from source using the latest clang and am trying it again, on the same machine, instead of using the official distribution. So far, 0 crashes in approximately 3,300 runs so far.

At the moment, then, the problem seems localized to the official 3.4.3 binaries for OS X.