multiselect dropdown in angularjs only works on initialization of Controller - angularjs

Question

I am using jquery, bootstrap multi-select dropdown. I want to populate multi-select dropdown (talukas) on selectionChange event of other normal (single-select) dropdown (city). I am not able to figure out why the multi select dropdown populates on initial load of a controller and why not on selection change of other dropdown. Can you please help me. Thank you.
Scenario - 1 => This works fine
<div ng-controller="tempController" ng-init="initializeController()" ng-cloak>
<select id="multiSelect" name="multiSelect" multiselect=""
multiple="" ng-model="selectedTalukas" ng-options="option.talukaId as
option.label for option in talukas"></select>
</div>
// .js
$scope.selectedTalukas = [];
$scope.initializeController = function () {
$scope.talukas = [
{ talukaId: 1, label: 'Taluka1' },
{ talukaId: 2, label: 'Taluka2' },
{ talukaId: 3, label: 'Taluka3' }
]
}
Scenario - 2 => This DO NOT works fine - WHY
<select id="city" class="form-control select2" name="ddlCity" ng-model="c" ng-options="c as c.name for c in city | orderBy:'name'"
ng-change="selectedCityChange(c)" >
</select>
<select id="multiSelect" name="multiSelect" multiselect=""
multiple="" ng-model="selectedTalukas" ng-options="option.talukaId as
option.label for option in talukas"></select>
$scope.selectedCityChange = function (selectedValue) {
if (selectedValue !== undefined) {
$scope.selectedCity = selectedValue;
$scope.selectedCityId = selectedValue.cityId;
$scope.ajaxPost(selectedValue.cityId,
'/api/Taluka/getTalukasForSelectedCity',
$scope.selectedCityChangeComplete,
$scope.selectedCityChangeError);
}
};
$scope.selectedCityChangeComplete = function (response) {
$scope.talukas = response.data.talukaMasters;
}