Mongos sends moveChunk command, balancer on config server schedules it, then config server steps down, interrupting the balancer at the point where the migration has been committed but waitForDelete has not finished on the shard. MigrationManager::executeManualMigration does a check on failure to see if the moveChunk was actually successful, and if so, sets the Status to OK.

If this is the case, we should not set Status to OK if the error is identifiably due to config interrupt/stepdown.