Python with threading core dumps on 5.3

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I am consistantly getting seg faults and bus errors when running a
multi threaded python application under 5.3-release-p2.  Python was
built from the port(python 2.4) with threading enabled.  Rebuilding
with the huge stack size option enabled didn't make a difference.  The
application uses twisted (www.twistedmatrix.com) and it runs fine
until I put it under a bit of a load and have 20-30 simultaneous
threads running.  Then it core dumps.  Following is the backtrace from
the core file.  The backtrace is always the same.  Are threads just
generally problematic on Freebsd?

#0  0x2823cdbb in pthread_testcancel () from /usr/lib/libpthread.so.1
#1  0x28234b06 in pthread_mutexattr_init () from /usr/lib/libpthread.so.1
#2  0x00000000 in ?? ()