"If you use ng-model, you have to have a dot in there."
Make your model point to an object.property and you'll be good to go.
Controller
$scope.formData = {};
$scope.check = function () {
console.log($scope.formData.searchText.$modelValue); //works
}
Template
<input ng-model="formData.searchText"/>
<button ng-click="check()">Check!</button>
This happens when child scopes are in play - like child routes or ng-repeats.
The child-scope creates it's own value and a name conflict is born as illustrated here:
See this video clip for more: https://www.youtube.com/watch?v=SBwoFkRjZvE&t=3m15s