The action this message is warning about is actually totally fine. The message should be removed.

Mon Oct 31 22:02:17 [WriteBackListener-HOST:PORT] warning: adding shard sub-connection HOST:PORT (parent SETNAME/HOST:PORT,HOST2:PORT2) as sharded, this is safe but unexpected
0x8201ae8 0x81feed0 0x81ff0a0 0x840937c 0x844299b 0x815e024 0x815f78e 0x845acdc 0xb7e86482 0xb7e0de9e
/usr/bin/mongos(_ZN5mongo17ClientConnections3getERKSsS2_b+0x5f8) [0x8201ae8]
/usr/bin/mongos(_ZN5mongo15ShardConnection5_initEb+0x70) [0x81feed0]
/usr/bin/mongos(_ZN5mongo15ShardConnectionC1ERKSsS2_b+0x80) [0x81ff0a0]
/usr/bin/mongos(_ZN5mongo10ClientInfo12getLastErrorERKNS_7BSONObjERNS_14BSONObjBuilderEb+0x1c9c) [0x840937c]
/usr/bin/mongos(_ZN5mongo17WriteBackListener3runEv+0x1b2b) [0x844299b]
/usr/bin/mongos(_ZN5mongo13BackgroundJob7jobBodyEN5boost10shared_ptrINS0_9JobStatusEEE+0xb4) [0x815e024]
/usr/bin/mongos(_ZN5boost6detail11thread_dataINS_3_bi6bind_tIvNS_4_mfi3mf1IvN5mongo13BackgroundJobENS_10shared_ptrINS7_9JobStatusEEEEENS2_5list2INS2_5valueIPS7_EENSD_ISA_EEEEEEE3runEv+0x7e) [0x815f78e]
/usr/bin/mongos(thread_proxy+0x7c) [0x845acdc]
/lib/i686/nosegneg/libpthread.so.0 [0xb7e86482]
/lib/i686/nosegneg/libc.so.6(clone+0x5e) [0xb7e0de9e]