How about you stop using filter and change it like this?

 <select class="form-control input-sm" style="width: 60px;">
    <option ng-selected="data.page.pageSize === 5">5</option>
    <option ng-selected="data.page.pageSize === 10" >10</option>
    <option ng-selected="data.page.pageSize === 20" >20</option>
    <option ng-selected="data.page.pageSize === 50" >50</option>
</select>

<select class="form-control input-sm" style="width: 60px;">
    <option data-ng-selected="{{data.page.pageSize | selected: 10}}" >10</option>
    <option data-ng-selected="{{data.page.pageSize | selected: 20}}" >20</option>
    <option data-ng-selected="{{data.page.pageSize | selected: 50}}" >50</option>
</select>


app.filter('selected', function() {
      return function(input, value) {
        return input == value;
      };
    })