https://jira.mongodb.org/browse/SERVER-6925 seems to show this was fixed in 2.2.1

Mon Nov 12 10:56:26 [rsSync] warning: DR102 too much data written uncommitted 314.577MB
0xaf8c41 0x731c01 0x731cdf 0x731fb2 0x7320cd 0x73213b 0x72bfba 0x80d386 0x65742b 0x65815c 0x80d197 0x80d488 0x859eee 0x81b65b 0x99762b 0x99e838 0x99ee18 0x99ee6a 0x99f27a 0xb3ec79
/usr/bin/mongod(_ZN5mongo15printStackTraceERSo+0x21) [0xaf8c41]
/usr/bin/mongod(_ZN5mongo3dur9CommitJob4noteEPvi+0x201) [0x731c01]
/usr/bin/mongod(_ZN5mongo3dur18ThreadLocalIntents8_unspoolEv+0x4f) [0x731cdf]
/usr/bin/mongod(_ZN5mongo3dur18ThreadLocalIntents7unspoolEv+0x52) [0x731fb2]
/usr/bin/mongod(_ZN5mongo3dur18ThreadLocalIntents4pushERKNS0_11WriteIntentE+0x6d) [0x7320cd]
/usr/bin/mongod(_ZN5mongo3dur11DurableImpl18declareWriteIntentEPvj+0x6b) [0x73213b]
/usr/bin/mongod(_ZN5mongo3dur11DurableImpl10writingPtrEPvj+0xa) [0x72bfba]
/usr/bin/mongod(_ZN5mongo16NamespaceDetails13addDeletedRecEPNS_13DeletedRecordENS_7DiskLocE+0x1a6) [0x80d386]
/usr/bin/mongod(_ZN5mongo16NamespaceDetails7compactEv+0x2eb) [0x65742b]
/usr/bin/mongod(_ZN5mongo16NamespaceDetails11cappedAllocEPKci+0x4bc) [0x65815c]
/usr/bin/mongod(_ZN5mongo16NamespaceDetails6_allocEPKci+0x27) [0x80d197]
/usr/bin/mongod(_ZN5mongo16NamespaceDetails5allocEPKciRNS_7DiskLocE+0x38) [0x80d488]
/usr/bin/mongod(_ZN5mongo11DataFileMgr17fast_oplog_insertEPNS_16NamespaceDetailsEPKci+0x6e) [0x859eee]
/usr/bin/mongod(_ZN5mongo11_logOpObjRSERKNS_7BSONObjE+0x27b) [0x81b65b]
/usr/bin/mongod(_ZN5mongo7replset8SyncTail15applyOpsToOplogEPSt5dequeINS_7BSONObjESaIS3_EE+0x4b) [0x99762b]
/usr/bin/mongod(_ZN5mongo7replset8SyncTail16oplogApplicationEv+0x388) [0x99e838]
/usr/bin/mongod(_ZN5mongo11ReplSetImpl11_syncThreadEv+0xb8) [0x99ee18]
/usr/bin/mongod(_ZN5mongo11ReplSetImpl10syncThreadEv+0x2a) [0x99ee6a]
/usr/bin/mongod(_ZN5mongo15startSyncThreadEv+0xaa) [0x99f27a]
/usr/bin/mongod() [0xb3ec79]