With Ember 0.9.8.1, in http://jsfiddle.net/MUuf6/1/, when clicking the link to apply the mixin to the view, the myBinding property does not seem to be initialized as a binding, as can be seen when clicking on 'Click me' after clicking on 'Include mixin'.
But the binding does get applied correctly when doing the same with 0.9.7.1 in http://jsfiddle.net/WcaYn/1/
Is this an expected change between 0.9.8.1 and 0.9.7.1?
Bindings have problems when applied to prototypes and reopen isn't designed for existing instances. It may have seemed to work before but it didn't without bugs. You should apply your mixin to the existing instance with apply().
Ah, good to know. Thanks!