emberjs/ember.js — pull request #4678 by sly7-7 (2014-04-09 15:19:43+00:00)
Title: [BUGFIX beta] pass context to sortFunction to avoid calling __nextSuper ...

...on undefined

May fix #4661, but I think there is a deeper cause around the __nextSuper thing.
The bug seems to appear only by calling ArrayProxy.createWithMixins(SortableMixin), and overriding the sortFunction.