Angular UI Bootstrap checkbox is not showing up checked

I have following code and its not showing up checked when clicked on checkbox.

<div class="col-xs-2 col-sm-2 col-md-2">
                                                                
                                        
                                        <div class="btn-group topFilterCtrl" dropdown dropdown-append-to-body
                                                
                                           
                                        >
                                                <div id="btn-append-to-body" type="button" class="btn btn-primary panelTextFont14 noBorder"          dropdown-toggle
                                                        ng-class="{'filterBarCommon' : !searchReservationVm.mouseondivStatus && !searchReservationVm.clickOnDivStatus, 
                                                    'filterBarCommonOnRollOver' : searchReservationVm.mouseondivStatus , 'filterBarCommonClick' : searchReservationVm.clickOnDivStatus}"
                                                    ng-mouseover="searchReservationVm.mouseondivStatus = true" 
                                                    ng-mouseleave="searchReservationVm.mouseondivStatus = false"
                                                    ng-focus="searchReservationVm.mouseondivStatus = true" 
                                                    ng-blur="searchReservationVm.mouseondivStatus = false" tabindex="2"
                                                    ng-click="searchReservationVm.showStatus()"
                                                    title="Status"
                                                >
                                                        {{searchReservationVm.statusCount}} Status<span class="caret caretFilterCtrl"></span>
                                                </div>
                                                <ul class="dropdown-menu customScroll" role="menu" aria-labelledby="btn-append-to-body"
                                                        ng-show="!searchReservationVm.displayStatus"    
                                                >
                                                        <li role="menuitem" class="changeColorOnHover"
                                                                ng-repeat="optionStatus in searchReservationVm.optionStatusList track by $index" ng-show="optionStatus.value != null">
                                                
                                                                <a href="#">
                                                                        <div class="checkbox" id="status{{$index-2}}"
                                                                                ng-show="optionStatus.value != null"
                                                                                ng-click="searchReservationVm.applyFilterForResultCount()"
                                                                                ng-change="searchReservationVm.getStatusCount(optionStatus)"
                                                                                ng-model="optionStatus.flag"
                                                                                >
                                                                                <label>
                                                                                        <input type="checkbox"
                                                                                                ng-click="searchReservationVm.clickStatusCheckBox(optionStatus)" 
                                                                                                ng-show="optionStatus.value != null"
                                                                                                />
                                                                                        {{optionStatus.value}}
                                                                                </label>
                                                                        </div>
                                                                </a>
                                                        </li>
                                                        <!--Clear div-->
                                                        <li role="menuitem" 
                                                                ng-click="searchReservationVm.clearAll()">
                                                                <a href="#">
                                                                        <p>
                                                                                <span style="color:#40A8E2;">Clear</span>
                                                                                <span style="color:#333333;">  – All Statuses</span>
                                                                        </p>
                                                                </a>
                                                        </li>
                                                </ul>
                                        </div>
                                        <span class="customLineDiv lineAtRight"></span>
                                </div>