I am curious as to why the record contained in the result set of a Model.save() response does not properly return updated associated data, despite the updated d
Completely agree with you. Really odd behavior. It should update the association store on the record. This is how i got around this issue (basically just run the response through the reader!):
success: function(record, operation) {
var newRecord= me.getMyModel().getProxy().reader.read(operation.response).records[0];
}