// DESCRIPTION //
Suppose there is a simple document with an 'tags' array:
_id : 7      51005201f8ab44f1690f9526
tags : 4     
    1 : 2    a
    2 : 2    b
    3 : 2    c
The server crashes when I try to append this array either via the '$push' or the '$addToSet' operator.
// LOGFILE OUTPUT //
Thu Jan 24 16:42:44 [conn1]  __test.test Assertion failure x == _nfields src\mongo\db\jsobj.cpp 1250
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\util\stacktrace.cpp(161)                           mongo::printStackTrace+0x3e
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\util\assert_util.cpp(109)                          mongo::verifyFailed+0xdc
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\db\jsobj.cpp(1250)                                 mongo::BSONIteratorSorted::BSONIteratorSorted+0xf3
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\db\ops\update_internal.cpp(906)                    mongo::ModSetState::createNewFromMods+0xa3
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\db\ops\update.cpp(370)                             mongo::_updateObjects+0x15a2
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\db\instance.cpp(573)                               mongo::receivedUpdate+0x60d
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\db\instance.cpp(437)                               mongo::assembleResponse+0x626
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\db\db.cpp(192)                                     mongo::MyMessageHandler::process+0xf5
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\mongo\util\net\message_server_port.cpp(86)               mongo::pms::threadRun+0x59a
Thu Jan 24 16:42:44 [conn1] mongod.exe    ...\src\third_party\boost\libs\thread\src\win32\thread.cpp(180)  boost::`anonymous namespace'::thread_start_function+0x21
Thu Jan 24 16:42:44 [conn1] mongod.exe    f:\dd\vctools\crt_bld\self_64_amd64\crt\src\threadex.c(314)      _callthreadstartex+0x17
Thu Jan 24 16:42:44 [conn1] mongod.exe    f:\dd\vctools\crt_bld\self_64_amd64\crt\src\threadex.c(292)      _threadstartex+0x7f
Thu Jan 24 16:42:44 [conn1] kernel32.dll                                                                   BaseThreadInitThunk+0xd
Thu Jan 24 16:42:44 [conn1] update __test.test query: { tags: "a" } update: { $push: { tags: "d" } } nscanned:1 keyUpdates:0 exception: assertion src\mongo\db\jsobj.cpp:1250 locks(micros) w:398335 399ms
Thu Jan 24 16:42:48 CTRL_CLOSE_EVENT signal
Thu Jan 24 16:42:48 [consoleTerminate] got CTRL_CLOSE_EVENT, will terminate after current cmd ends
Thu Jan 24 16:42:48 [consoleTerminate] now exiting
Thu Jan 24 16:42:48 dbexit: 
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: going to close listening sockets...
Thu Jan 24 16:42:48 [consoleTerminate] closing listening socket: 496
Thu Jan 24 16:42:48 [consoleTerminate] closing listening socket: 516
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: going to flush diaglog...
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: going to close sockets...
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: waiting for fs preallocator...
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: lock for final commit...
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: final commit...
Thu Jan 24 16:42:48 [conn1] end connection 127.0.0.1:52419 (0 connections now open)
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: closing all files...
Thu Jan 24 16:42:48 [consoleTerminate] closeAllFiles() finished
Thu Jan 24 16:42:48 [consoleTerminate] journalCleanup...
Thu Jan 24 16:42:48 [consoleTerminate] removeJournalFiles
Thu Jan 24 16:42:48 [consoleTerminate] shutdown: removing fs lock...
Thu Jan 24 16:42:48 dbexit: really exiting now