Inconsistent results returned with unique index

[cyberwombat]

Basically if I have a field with unique:true then trying to fetch all results returns a random amount of items. I have 4013 items in the db. Here's the schema.

var Order = new Schema({
 code: {
  type: String,
  unique: true
},
...
});

Now run some queries:

Order.find().exec(function(err, orders) {
 console.log(orders.length); // always 101 
})

Order.find().limit(100000).exec(function(err, orders) {
 console.log(orders.length); // varies, sometimes 1150, 1790, 2046 - never more
})

Now if I remove the 'unique: true' from schema it will always return the total amount:

Order.find().exec(function(err, orders) {
 console.log(orders.length); // always 4013 (correct total)
})

Any idea as to why this behavior occurs? afaik the codes are all unique (orders from a merchant). This is tested on 3.8.6, 3.8.8

[cyberwombat]

Here's my guess - there are duplicate items in there and Mongo is freaking out and choking in a sync way - it never gets higher than 2046 whichI bet is a duplicate - a few times it will stop early so I think it a) stops on duplicate and b) it does so sync or not in same "process" as fetching and will sometimes stop earlier. I bet if I remove the dups it will prob work though I wish there was some errors. Does that sound about right?

[cyberwombat]

I am guessing it's related to this #1225