When a server in a replica set steps down from its primary role while certain metadata commands are actively running, the server may shut down. Such commands include mapReduce, renameCollection, dropDatabase, drop, dropIndexes, emptyCapped, convertToCapped, collMod, and create.
Replica sets with a sufficient majority should continue to operate normally after a new primary is elected, but any metadata write operations in progress are lost and not replicated. The affected server can be restarted as a secondary.
MongoDB 2.6.0 and 2.6.1 production releases are affected by this issue.
The fix is included in the 2.6.2 production release.
Apply proper locking semantics around metacommands to synchronize with replica set stepdown.