This is the same issue as highlighted by Issue6676.  The root cause is attempting to reuse a parser instance and that is known to not work with the version of expat included with Python.  Whether the test program crashes with a memory access violation or just uses uninitialized memory depends on the version of malloc in use and what protections the linker and os use.  Even on Mac OS X, the test program does not segfault on earlier versions of OS X (like 10.5).  And on 10.6 and 10.7 if you build python with pymalloc it usually does not segfault.  But that doesn't mean it is working properly.  At a minimum, the single use restriction should be documented; if anyone is interested, they could look into adding any more recent fixes to expat and plugging remaining reuse holes.