Problem with BindingUtils.bindSetter

I am not getting the expected functionality from BindingUtils.bindSetter.
here is relative code:

BindingUtils.bindSetter(onLoaded, _model.someObject,
"propertyOnSomeObject");

someObject is a bindable class.

public function onLoaded(value:Object):void

if (value) // it only gets here once when value is null

I am getting into the setter when a value is not null.
But I see that _model.someObject gets its value when a proper event is
fired.
My question is why it does not go into the listener where there is a value?

Thanks