Can you trim down your example a bit to make it easier to identify the problem. The bare minimum, without controls, would be helpful. Also include exactly what I need to do to see the error, what the error is, and what is expected.
Live binding doesn't copy properties to _data, can.Observe does that. But that's necessary. It's the copying of those same properties to the object itself for reading purposes that is unnecessary (but necessary for backwards compliance with JMVC). This could be removed by overwriting __set:
https://github.com/bitovi/canjs/blob/master/observe/observe.js#L705 to remove the
if (!(prop in this.constructor.prototype)) { part. You will always have to read via .attr.
If you're not using setters (and setting up child observes yourself), it's likely possible to bypass copying each property directly and just set the data as this._data.