AngularJS add variable to scope problems

I am working on a more complex project(10000+ LoC) and during development I encountered a problem very often.

When I add a simple variable to scope like: $scope.editing = true;

   $sope.editing=false;

   $scope.changeTextButtonClicked = function() {
         $scope.editText;
   } 

   <span ng-hide="editing">{{editText}}</span>
   <input type="text" ng-model="editText" ng-show="editing">
   <input type ="button" ng-click="changeTextButtonClicked()">

The current value of $scope.editText can't be accessed from the controllers javascript code! In some cases I got the old value when accessing $scope.editText like the DOM is not updated but when printing it directly on the website with {{editText}} it works and gets updated but in the controller I get the old value.

It happened that I have one value for {{editText}} on the website and another value for $scope.editText in the controller (invalid one - previous).

I solved this with adding it to a data array or any other array that is nested inside the scope:

     $scope.data={}
     $scope.data.editText = ...;

Can anybody explain to me why it works sometimes with $scope.variable and sometime it doesn't and you need to add $scope.**foobar**.variable?