openlayers 3 featureKey exists in featureChangeKeys - openlayers-3

Question

I have an ol.interaction.Select acting on an ol.source.Vector which is within an ol.layer.Vector. I can select and unselect individual countries fine. I am using a dragbox to select multiple countries. If I select anywhere outside of the multiply selected countries, the currently selected get unselected. Excellent!
However, the problem is that if I select a currently selected country within the multiple, I get the AssertionError: Assertion failed: featureKey exists in featureChangeKeys
Here's my Vector layer:
_countrySelectSource = new ol.source.Vector({
url: 'vendor/openlayers/geojson/countries.json',
format: new ol.format.GeoJSON()
});
var countryLayer = new ol.layer.Vector({
title: 'Country Select',
visible: true,
type: 'interactive-layers',
source: _countrySelectSource
});
I add countryLayer to my map, _map.
I then create a _CountrySelect object that allows me to setActive(true|false) on the interactions related to my country selection.
_CountrySelect = {
init : function(){
this.select = new ol.interaction.Select();
_map.addInteraction(this.select);
this.dragbox = new ol.interaction.DragBox({
condition: ol.events.condition.platformModifierKeyOnly
});
_map.addInteraction(this.dragbox);
this.setEvents();
},
setEvents: function(){
var selectedFeatures = this.select.getFeatures();
var infoBox = document.getElementById('info');
var selfDragbox = this.dragbox;
selfDragbox.on('boxend', function() {
// features that intersect the box are added to the collection of
// selected features, and their names are displayed in the "info"
// div
var extent = selfDragbox.getGeometry().getExtent();
_countrySelectSource.forEachFeatureIntersectingExtent(extent, function(feature) {
selectedFeatures.push(feature);
_countryCodes.push(feature.getId());
});
infoBox.innerHTML = _countryCodes.join(', ');
});
// clear selection when drawing a new box and when clicking on the map
selfDragbox.on('boxstart', function() {
selectedFeatures.clear();
infoBox.innerHTML = ' ';
});
_map.on('singleclick', function(event) {
selectedFeatures.clear();
_countryCodes = [];
_map.forEachFeatureAtPixel(event.pixel,function(feature){
selectedFeatures.push(feature);
var id = feature.getId();
var index = _countryCodes.indexOf(id);
if ( index === -1 ) {
_countryCodes.push(feature.getId());
}
});
infoBox.innerHTML = _countryCodes.join(', ');
});
},
setActive: function(active){
this.select.setActive(active);
this.dragbox.setActive(active);
}
};
_CountrySelect.init();
I am not sure if this is an issue with OL3 or my code. Maybe there's an event I'm not handling? Maybe it's the ol.interaction.DragBox (no luck researching on the DragBox). Let me know what further information I can provide.