... and this can cause the buildbot to fail:
m30001| Thu Sep 6 12:51:49 [conn6] Assertion failure ! _active src/mongo/s/d_migrate.cpp 266
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo10logContextEPKc+0x5b) [0x8801b6d]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo12verifyFailedEPKcS1_j+0xff) [0x8983dc9]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo17MigrateFromStatus5startERKSsRKNS_7BSONObjES5_S5_+0x6c) [0x868c230]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo16MoveChunkCommand3runERKSsRNS_7BSONObjEiRSsRNS_14BSONObjBuilderEb+0x261d) [0x869099f]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo12_execCommandEPNS_7CommandERKSsRNS_7BSONObjEiRNS_14BSONObjBuilderEb+0x71) [0x86b46e4]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo11execCommandEPNS_7CommandERNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0x9ae) [0x86b5344]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x32e) [0x86b5c68]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo11runCommandsEPKcRNS_7BSONObjERNS_5CurOpERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x49) [0x864f545]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo19MigrateStatusHolderC1ERKSsRKNS_7BSONObjES5_S5_+0x3c) [0x868e012]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod() [0x895bb78]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE+0x2e9) [0x895cb29]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE+0xb2) [0x853652e]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo3pms9threadRunEPNS_13MessagingPortE+0x557) [0x89c8157]
m30001| /home/yellow/buildslave/Linux_32bit_debug/mongo/mongod(_ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1_+0x3d1) [0x8654049]
m30001| /lib/libc.so.6(clone+0x5e) [0xca6d4e]
m30001| /lib/libpthread.so.0() [0xd5d919]
m30001|
m30001| ***aborting after verify() failure as this is a debug/test build
m30001|
m30001|
m30001| Thu Sep 6 12:51:49 Got signal: 6 (Aborted).
http://buildlogs.mongodb.org/build/5048b7bad2a60f066b000140/test/5048e16ad2a60f7823000b5f/
from http://buildbot.mongodb.org/builders/Linux%2032-bit%20debug