Since CanJS 1.1.8 (we migrated from 1.1.6 to 2.0.4), options.contexts is no longer an array but an instance of Scope which implements a linked-list paradigm.  Index references will no longer work.  If you want to add a context to the scope chain, use options.contexts.add().  This creates a new Scope that points to the original; it doesn't modify the original one.