I would need to see your controller to confirm, but you are likely clobbering your date. In your controller, I am assuming you have something like
$scope.date = "03/11/2014";
Instead, do something like this
$scope.foo = { "date":"03/11/2014"}
and update your html to
<input type="text" ng-model="foo.date" required>
Now when the user updates the input, it won't clobber the other "date" reference, but instead just update the date property of the foo reference. Checkout this quick video for an explanation. https://egghead.io/lessons/angularjs-the-dot