Thank you for clarifying that.
This happens because the updated field should match the source binding in order to redraw the template. Using the "self.set('event.id', id)" notation will update the event object, however the updated field will be "event.id", which does not match the div's source binding. In this case you can use an approach similar to what I previously suggested - either update the whole object or trigger the change event manually and specify the updated field:
'Ski Martock, March 2nd, 2015'
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