I have not found a repro yet, but it happens when I quit the shell (via ctrl-c) or sometimes when run a smoke test. It does not happen consistently.

Here is an example stacktrace:
ReplSetTest stopSet *** Shut down repl set - test worked ****
mongo got signal 11 (Segmentation fault), stack trace:
0x70a916 0x5c2626 0x7fecea455240 0x9a7981 0x7e2b57 0x8a8455 0x8a82c6 0x6bf1fc 0x6bf0cc 0x5cc896 0x5ccdf9 0x7fecea441a15 0x5c1399
/home/dannenberg/work/server10086/mongo/mongo(_ZN5mongo15printStackTraceERSo+0x26) [0x70a916]
/home/dannenberg/work/server10086/mongo/mongo(_Z12quitAbruptlyi+0x1f6) [0x5c2626]
/usr/lib/libc.so.6(+0x35240) [0x7fecea455240]
/home/dannenberg/work/server10086/mongo/mongo(_ZN2v88internal15MemoryAllocator4FreeEPNS0_11MemoryChunkE+0x41) [0x9a7981]
/home/dannenberg/work/server10086/mongo/mongo(_ZN2v88internal15DeoptimizerDataD1Ev+0x27) [0x7e2b57]
/home/dannenberg/work/server10086/mongo/mongo(_ZN2v88internal7Isolate6DeinitEv+0x65) [0x8a8455]
/home/dannenberg/work/server10086/mongo/mongo(_ZN2v88internal7Isolate8TearDownEv+0x56) [0x8a82c6]
/home/dannenberg/work/server10086/mongo/mongo(_ZN5mongo7V8ScopeD1Ev+0x10c) [0x6bf1fc]
/home/dannenberg/work/server10086/mongo/mongo(_ZN5mongo7V8ScopeD0Ev+0xc) [0x6bf0cc]
/home/dannenberg/work/server10086/mongo/mongo(Z5_mainiPPcS0+0x8566) [0x5cc896]
/home/dannenberg/work/server10086/mongo/mongo(main+0x59) [0x5ccdf9]
/usr/lib/libc.so.6(__libc_start_main+0xf5) [0x7fecea441a15]
/home/dannenberg/work/server10086/mongo/mongo() [0x5c1399]