Checkbox not working with Bootstrap in AnularJS

I have a Checkbox which is not getting checked if I keep it inside the div tag

<div class="col-xs-8 col-sm-8 col-md-8 col-lg-8">
<label class="lbl" for="a">Fee</label>
</div>
<div class="col-xs-4 col-sm-4 col-md-4 col-lg-4">
<input type="checkbox" id="a" ng-model="x.y" />
</div>

where as it works perfectly when I remove it from the div tag.

<div class="col-xs-8 col-sm-8 col-md-8 col-lg-8">
<label class="lbl" for="a">Fee</label>
</div>
<input type="checkbox" id="a" ng-model="x.y">

Why is it so? How can div tag affect the behavior of check-boxes. Note: I am not using any inline style nor am I overloading any pre-defined class.