How to work around property('controllers.man.filter') not working

I have a controller used inside #each that has needs:'man' and a property that declares .property('controllers.man.filter'). This property is not reevaluated when the 'filter' property of the 'man' controller changes.

Is it by design or should I look for a bug somewhere in my code?

I work around that adding observer in 'init' and removing it in 'destroy' of my controller.

Is it a sane way to react to changes in the upper controller?