moxi crash in drive_machine

During weekend testing, I saw osx console report a moxi crash in drive_machine.
Only ever saw this once.

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Process: moxi-debug [41532]
Path: /Users/steveyen/work/northscale/dev/wallace_master/components/tmp/repo_moxi/moxi/moxi-debug
Identifier: moxi-debug
Version: ??? (???)
Code Type: X86-64 (Native)
Parent Process: beam.smp [41479]

Date/Time: 2010-07-18 20:43:50.895 -0700
OS Version: Mac OS X 10.6.3 (10D578)
Report Version: 6

Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000027
Crashed Thread: 1

Thread 0: Dispatch queue: com.apple.main-thread
0 libSystem.B.dylib 0x00007fff841bc4ea kevent + 10
1 libevent-1.4.2.dylib 0x0000000100111213 kq_dispatch + 83
2 libevent-1.4.2.dylib 0x0000000100104d28 event_base_loop + 440
3 moxi 0x00000001000179c6 main + 7022
4 moxi 0x0000000100000f04 start + 52

Thread 1 Crashed:
0 moxi 0x0000000100013e82 drive_machine + 5734
1 moxi 0x000000010001459a event_handler + 285
2 libevent-1.4.2.dylib 0x0000000100105031 event_base_loop + 1217
3 moxi 0x000000010001fcad worker_libevent + 274
4 libSystem.B.dylib 0x00007fff841dc8b6 _pthread_start + 331
5 libSystem.B.dylib 0x00007fff841dc769 thread_start + 13