I have noticed that one-time binding with :: always wants to deep-copy objects in an expression, whereas normal binding will simply store and compare a reference.

Minimal example: http://jsfiddle.net/mhelvens/PXdkK/1/

This example demonstrates the inconsistent behavior by binding to an object that holds a reference to a $scope. The one-time binding prompts an ng:cpws error, indicating that a deep copy is being made.

I would prefer the traditional behavior for various reasons. But in any case, I assume that this inconsistency was not deliberate.