There seems to be some sort of error, the failure looks like:

2013-11-06T10:23:53.645-0500 error:

{ "$err" : "error querying server", "code" : 15988 }

at src/mongo/shell/query.js:131

Known failures:

http://mci.10gen.com/ui/task/mongodb_mongo_master_osx_108_cxx11_debug_0f7bd3d2d308ea2c7c154977bde301c87129d0df_13_11_06_00_13_24_aggregation_osx_108

http://mci.10gen.com/ui/task/mongodb_mongo_master_osx_108_cxx11_debug_dcd569ac549275cd3b81642325f63001cb33cd64_13_11_06_15_00_07_aggregation_osx_108