Mongoose Sorting issue

I have a collection

var mycoll = new Schema({
    col1: { type: String,required: true,}
  , col2: {type: String} 
  , mydate: {type: Date, required: true, default: Date.now,index:1} 
  etcetc
}, { collection: 'info' });

I a building a query based on mongoose like below

Info.statics.FindbyPage= function (callback, skip, limit) {

var infos = this.find();

infos.sort({ mydate: 1}).skip(skip).limit(limit);

res = infos.exec(callback)

}

the problem is that the result is not sorted by mydate, if i remove the limit and skip things the results will load all and they're well sorted once i put skip and limit the resutls is sorted but some date are missing ...

any help??? one thing to notice is i tried every possibilty in the sort param

i am using mongoose v3