Ember.Select cannot observe change to selection variable of dynamically generated control

I am dynamically building a number of select controls. I want to know when an option has changed so I am doing the following:

The idea there is that I dynamically create properties on the selections object which is used to hold the selected values.

//Add observer
Ember.defineProperty(selections, camelizedModelClass, null);
selections.addObserver(camelizedModelClass, self, 'selectionChanged');

Here is the function that should be called when selection has changed.

selectionChanged : function(sender, key, value, rev) {
    console.log('worked!');
},

In my template I create Ember.Select's as follows.

{{#each control in controls}}

    <div {{bind-attr class=":form-group control.width"}}>
        <label for="exampleInputPassword1">{{control.label}}</label>
        {{view "select"
        content=control.content
        selection=control.selection
        optionValuePath=control.optionValuePath
        optionLabelPath=control.optionLabelPath
        class = "form-control"
        prompt=control.prompt
        }}
        <p class="help-block"></p>
    </div>

{{/each}}

Each control in the controls array has the following property.

selection: 'selections.' + camelizedModelClass,

The observer method is never called, however, if I manually enter the selection as follows it is in fact called.

{{view "select"
content=control.content
selection=selections.manager
optionValuePath=control.optionValuePath
optionLabelPath=control.optionLabelPath
class = "form-control"
prompt=control.prompt
}}

Why is this not working? The other weird thing is that if I put {{control.selection}} in my handlebars template I can see the model changing for the first method but not the second.