> db.bar.drop()
true
> db.bar.insert({_id: 0, a: [8], b: 1})
WriteResult({ "nInserted" : 1 })
> db.bar.insert({_id: 1, a: [6, 10], b: 1})
WriteResult({ "nInserted" : 1 })
> db.bar.ensureIndex({a: 1})
{
	"createdCollectionAutomatically" : false,
	"numIndexesBefore" : 1,
	"numIndexesAfter" : 2,
	"ok" : 1
}
> db.bar.find({$or: [{a: {$gt: 7}}, {a: {$gt: 6}}]}).sort({a: 1}) // SORT_MERGE not used: correct order.
{ "_id" : 0, "a" : [ 8 ], "b" : 1 }
{ "_id" : 1, "a" : [ 6, 10 ], "b" : 1 }
> db.bar.find({$or: [{a: {$gt: 7}, b: 1}, {a: {$gt: 6}, b: 1}]}).sort({a: 1}) // SORT_MERGE used: incorrect order.
{ "_id" : 1, "a" : [ 6, 10 ], "b" : 1 }
{ "_id" : 0, "a" : [ 8 ], "b" : 1 }