angularjs ui-bootstrap 2 datepickers is error

i used uibootstraps datepicker,i write 2 in a page. 1 is starttime ,1 is endtime i want when i set starttime ,the endtimes min-date is start time. but when i click ,endtime will get empty in first time,and its ok in second time.

   <p class="input-group">
              <input  class="form-control" datepicker-popup ng-model="view.starttime" is-open="dateSet.opened.startTime" min-date="'2015-05-02'" max-date="'2015-06-22'" datepicker-options="dateSet.dateOptions" date-disabled="dateSet.disabled(date, mode)" ng-required="true" show-weeks="flase" />
              <span class="input-group-btn">
                <button type="button" class="btn btn-default" ng-click="dateSet.openFn($event,'startTime')"><i class="glyphicon glyphicon-calendar"></i></button>
              </span>
            </p>
 <p class="input-group">
                  <input  class="form-control" datepicker-popup ng-model="view.endtime" is-open="dateSet.opened.endTime" min-date="view.starttime" max-date="'2015-06-22'" datepicker-options="dateSet.dateOptions" date-disabled="dateSet.dateSet.disabled(date, mode)" ng-required="true" show-weeks="flase"/>
                  <span class="input-group-btn">
                    <button type="button" class="btn btn-default" ng-click="dateSet.openFn($event,'endTime')"><i class="glyphicon glyphicon-calendar"></i></button>
                  </span>
                </p>