mongoose instance method is undefined AFTER correctly ordering method definition and schema naming

I defined an instance method on a schema that I can't seem to access. Before I go into details, I'll say that I have read [this question] (Mongoose instance method is undefined), which had the same problem, but my root cause must be different. I defined all instance methods before I connected the model to its name.

First I defined a schema, and then defined an instance method: AccountSchema.methods.addFunds = function(amountToAd, callback) { // do some stuff to add funds return callback(); }

At the bottom of that file, I associate the name to the schema: var exports = module.exports = Account = mongoose.model('Account', AccountSchema);

For the record, just before associating the schema and name, I checked to make sure that AccountSchema.methods had my instance method.

Later, I use Account.findOne to fetch an instance of an account:

AccountSchema.statics.login = function( email, password, callback) { 
Account.findOne({ email:email}, function( err, doc){
        if(err) {
            console.log(err, null);
        } 

        // below is just some stuff to see if the doc is associated to the schema
        if(doc) {
            var keys = Object.keys(doc.schema);
            for(var propertyName in doc.schema) {
            console.log(propertyName + ":  " + doc[propertyName]);
        }
        // blah, do some other stuff
        callback(doc);
    }
}

I include the snippet above because it looks like at the time I fetched the account from my db, it no longer has any instance methods.

Finally, when I try to call doc.addFunds, I get:

TypeError: Object #<Object> has no method 'addFunds'

I'd appreciate any help or a link to a fully complete mongoose schema definition that uses instance methods.