Having a <select> and ng-options with a group by clause, after an update of the list (e.g. using a filter) the rendered list (of <optgroup>/<option>) isn't cleared but gets longer and longer after each update (IE11).

<select size="20" ng-model="selected" 
  ng-options="i as i.name group by i.cls for i in list | filter:filter">
</select>

Steps to reproduce:

1. Open https://jsfiddle.net/gk8xeupm/ with IE11
2. Type "foo" into the filter text field
3. Clear text field
4. Type "bar" into the filter text field
5. Clear text field
6. Watch the list becoming longer and longer

AngularJS: 1.4.8
Reproducable: always
Operating System: Windows 10
Browsers: IE version 11.11.10586.0