overzealous filter on nested ng-repeat - angularjs-ng-repeat

Question

I have a series of ng-repeated ul/li sets, and I want to make one set of li's visible when a link at the ul level is clicked.
My code is based around the answer found here: https://stackoverflow.com/a/12431211 which suggests that model mutation is the right way to do this.
The filter seems to be more zealous than anticipated, and I end up with nothing.
How can I achieve this functionality?
div ng-controller="DeviceController">
<ul ng-repeat="category in devices">
<a ng-click="setCategory(category)">{{category.name}}</a>
<li ng-repeat="device in selected.devices | filter: isSelected(category)">
{{device.name}}
</li>
</ul>
</div>
function DeviceController($scope) {
$scope.devices = [
{name: 'Desktop',
devices: [{id:1, name:'Olivia'},
{id:2, name:'Cayenne'}]
},
{name: 'Laptop',
devices: [{id:3, name:'Probook'},
{id:4, name:'Asus G750'}]
},
{name: 'Tablet',
devices: [{id:5, name:'Transformer Prime'},
{id:4, name:'Galaxy Note 10.1'}]
}
];
$scope.setCategory = function(category) {
$scope.selected = category
}
$scope.isSelected = function(category) {
return $scope.selected === category;
}
}
fiddle is here: http://jsfiddle.net/3rV6w/6/
I can't figure out why that isSelected() function works well as a condition on the active class (in the referenced answer) but doesn't perform equally as a filter. Scope perhaps? various console.log's suggest that it should work, but..

Answer 1

I've ended up discarding the filter, and using ng-hide instead.
<ul ng-repeat="category in devices">
<a ng-click="setCategory(category)">{{category.name}}</a>
<li ng-repeat="device in selected.devices" ng-hide="!isSelected(category)">
{{device.name}}
</li>
</ul>
What I think was happening is that the ng-filter was comparing 'device' with the true/false returned by isSelected(category). This will never match, so no results made it past the filter.