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    Type:Bug 
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    Resolution: Done
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    Priority:Major - P3 
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    Affects Version/s: 2.8.0-rc2
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    Component/s: Index Maintenance
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    None
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        Fully Compatible
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        ALL
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        None
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        None
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        None
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        None
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        None
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        None
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        None
One way to reproduce:
Start server with setting "failIndexKeyTooLong" set to false and try to sync from a 2.6 primary which has too long keys indexed, 2.8 secondary fails with:
2014-12-09T05:56:39.090+0000 I INDEX    [rsSync] Btree::insert: key too large to index, failing db.coll.etc { : "                                                                                                                                                      ..." }
2014-12-09T05:56:39.090+0000 D -        [rsSync] User Assertion: 17280:Btree::insert: key too large to index, failing db.coll"                                                                                                                                                      ..." }
2014-12-09T05:56:39.136+0000 D STORAGE  [rsSync] db.coll.etc: clearing plan cache - collection info cache reset
2014-12-09T05:56:39.209+0000 D STORAGE  [rsSync] db.coll.etc: clearing plan cache - collection info cache reset
2014-12-09T05:56:39.295+0000 E REPL     [rsSync] 17280 Btree::insert: key too large to index, failing db.collection etc. "                                                                                                                                                      ..." }
2014-12-09T05:56:39.295+0000 E REPL     [rsSync] initial sync attempt failed, 9 attempts remaining