Track repeater by index on rating template

AngularJS 1.2 throws this error on the rating directive:

Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater: r in range, Duplicate key: object:008
http://errors.angularjs.org/1.2.0-rc.2/ngRepeat/dupes?p0=r%20in%20range&p1=object%3A008

Following the pointers specified in the doc (as in track by var) works.
I'm not sure about backwards compatibility as i'm new to AngularJS.